Python/ast.c

/*
 * This file includes functions to transform a concrete syntax tree (CST) to
 * an abstract syntax tree (AST). The main function is PyAST_FromNode().
 *
 */
#include "Python.h"
#include "Python-ast.h"
#include "node.h"
#include "ast.h"
#include "token.h"

#include <assert.h>

static int validate_stmts(asdl_seq *);
static int validate_exprs(asdl_seq *, expr_context_ty, int);
static int validate_nonempty_seq(asdl_seq *, const char *, const char *);
static int validate_stmt(stmt_ty);
static int validate_expr(expr_ty, expr_context_ty);

static int
validate_comprehension(asdl_seq *gens)
{
    int i;
    if (!asdl_seq_LEN(gens)) {
        PyErr_SetString(PyExc_ValueError, "comprehension with no generators");
        return 0;
    }
    for (i = 0; i < asdl_seq_LEN(gens); i++) {
        comprehension_ty comp = asdl_seq_GET(gens, i);
        if (!validate_expr(comp->target, Store) ||
            !validate_expr(comp->iter, Load) ||
            !validate_exprs(comp->ifs, Load, 0))
            return 0;
    }
    return 1;
}

static int
validate_slice(slice_ty slice)
{
    switch (slice->kind) {
    case Slice_kind:
        return (!slice->v.Slice.lower || validate_expr(slice->v.Slice.lower, Load)) &&
            (!slice->v.Slice.upper || validate_expr(slice->v.Slice.upper, Load)) &&
            (!slice->v.Slice.step || validate_expr(slice->v.Slice.step, Load));
    case ExtSlice_kind: {
        int i;
        if (!validate_nonempty_seq(slice->v.ExtSlice.dims, "dims", "ExtSlice"))
            return 0;
        for (i = 0; i < asdl_seq_LEN(slice->v.ExtSlice.dims); i++)
            if (!validate_slice(asdl_seq_GET(slice->v.ExtSlice.dims, i)))
                return 0;
        return 1;
    }
    case Index_kind:
        return validate_expr(slice->v.Index.value, Load);
    default:
        PyErr_SetString(PyExc_SystemError, "unknown slice node");
        return 0;
    }
}

static int
validate_keywords(asdl_seq *keywords)
{
    int i;
    for (i = 0; i < asdl_seq_LEN(keywords); i++)
        if (!validate_expr(((keyword_ty)asdl_seq_GET(keywords, i))->value, Load))
            return 0;
    return 1;
}

static int
validate_args(asdl_seq *args)
{
    int i;
    for (i = 0; i < asdl_seq_LEN(args); i++) {
        arg_ty arg = asdl_seq_GET(args, i);
        if (arg->annotation && !validate_expr(arg->annotation, Load))
            return 0;
    }
    return 1;
}

static const char *
expr_context_name(expr_context_ty ctx)
{
    switch (ctx) {
    case Load:
        return "Load";
    case Store:
        return "Store";
    case Del:
        return "Del";
    case AugLoad:
        return "AugLoad";
    case AugStore:
        return "AugStore";
    case Param:
        return "Param";
    default:
        assert(0);
        return "(unknown)";
    }
}

static int
validate_arguments(arguments_ty args)
{
    if (!validate_args(args->args))
        return 0;
    if (args->vararg && args->vararg->annotation
        && !validate_expr(args->vararg->annotation, Load)) {
            return 0;
    }
    if (!validate_args(args->kwonlyargs))
        return 0;
    if (args->kwarg && args->kwarg->annotation
        && !validate_expr(args->kwarg->annotation, Load)) {
            return 0;
    }
    if (asdl_seq_LEN(args->defaults) > asdl_seq_LEN(args->args)) {
        PyErr_SetString(PyExc_ValueError, "more positional defaults than args on arguments");
        return 0;
    }
    if (asdl_seq_LEN(args->kw_defaults) != asdl_seq_LEN(args->kwonlyargs)) {
        PyErr_SetString(PyExc_ValueError, "length of kwonlyargs is not the same as "
                        "kw_defaults on arguments");
        return 0;
    }
    return validate_exprs(args->defaults, Load, 0) && validate_exprs(args->kw_defaults, Load, 1);
}

static int
validate_expr(expr_ty exp, expr_context_ty ctx)
{
    int check_ctx = 1;
    expr_context_ty actual_ctx;

    /* First check expression context. */
    switch (exp->kind) {
    case Attribute_kind:
        actual_ctx = exp->v.Attribute.ctx;
        break;
    case Subscript_kind:
        actual_ctx = exp->v.Subscript.ctx;
        break;
    case Starred_kind:
        actual_ctx = exp->v.Starred.ctx;
        break;
    case Name_kind:
        actual_ctx = exp->v.Name.ctx;
        break;
    case List_kind:
        actual_ctx = exp->v.List.ctx;
        break;
    case Tuple_kind:
        actual_ctx = exp->v.Tuple.ctx;
        break;
    default:
        if (ctx != Load) {
            PyErr_Format(PyExc_ValueError, "expression which can't be "
                         "assigned to in %s context", expr_context_name(ctx));
            return 0;
        }
        check_ctx = 0;
        /* set actual_ctx to prevent gcc warning */
        actual_ctx = 0;
    }
    if (check_ctx && actual_ctx != ctx) {
        PyErr_Format(PyExc_ValueError, "expression must have %s context but has %s instead",
                     expr_context_name(ctx), expr_context_name(actual_ctx));
        return 0;
    }

    /* Now validate expression. */
    switch (exp->kind) {
    case BoolOp_kind:
        if (asdl_seq_LEN(exp->v.BoolOp.values) < 2) {
            PyErr_SetString(PyExc_ValueError, "BoolOp with less than 2 values");
            return 0;
        }
        return validate_exprs(exp->v.BoolOp.values, Load, 0);
    case BinOp_kind:
        return validate_expr(exp->v.BinOp.left, Load) &&
            validate_expr(exp->v.BinOp.right, Load);
    case UnaryOp_kind:
        return validate_expr(exp->v.UnaryOp.operand, Load);
    case Lambda_kind:
        return validate_arguments(exp->v.Lambda.args) &&
            validate_expr(exp->v.Lambda.body, Load);
    case IfExp_kind:
        return validate_expr(exp->v.IfExp.test, Load) &&
            validate_expr(exp->v.IfExp.body, Load) &&
            validate_expr(exp->v.IfExp.orelse, Load);
    case Dict_kind:
        if (asdl_seq_LEN(exp->v.Dict.keys) != asdl_seq_LEN(exp->v.Dict.values)) {
            PyErr_SetString(PyExc_ValueError,
                            "Dict doesn't have the same number of keys as values");
            return 0;
        }
        /* null_ok=1 for keys expressions to allow dict unpacking to work in
           dict literals, i.e. ``{**{a:b}}`` */
        return validate_exprs(exp->v.Dict.keys, Load, /*null_ok=*/ 1) &&
            validate_exprs(exp->v.Dict.values, Load, /*null_ok=*/ 0);
    case Set_kind:
        return validate_exprs(exp->v.Set.elts, Load, 0);
#define COMP(NAME) \
        case NAME ## _kind: \
            return validate_comprehension(exp->v.NAME.generators) && \
                validate_expr(exp->v.NAME.elt, Load);
    COMP(ListComp)
    COMP(SetComp)
    COMP(GeneratorExp)
#undef COMP
    case DictComp_kind:
        return validate_comprehension(exp->v.DictComp.generators) &&
            validate_expr(exp->v.DictComp.key, Load) &&
            validate_expr(exp->v.DictComp.value, Load);
    case Yield_kind:
        return !exp->v.Yield.value || validate_expr(exp->v.Yield.value, Load);
    case YieldFrom_kind:
        return validate_expr(exp->v.YieldFrom.value, Load);
    case Await_kind:
        return validate_expr(exp->v.Await.value, Load);
    case Compare_kind:
        if (!asdl_seq_LEN(exp->v.Compare.comparators)) {
            PyErr_SetString(PyExc_ValueError, "Compare with no comparators");
            return 0;
        }
        if (asdl_seq_LEN(exp->v.Compare.comparators) !=
            asdl_seq_LEN(exp->v.Compare.ops)) {
            PyErr_SetString(PyExc_ValueError, "Compare has a different number "
                            "of comparators and operands");
            return 0;
        }
        return validate_exprs(exp->v.Compare.comparators, Load, 0) &&
            validate_expr(exp->v.Compare.left, Load);
    case Call_kind:
        return validate_expr(exp->v.Call.func, Load) &&
            validate_exprs(exp->v.Call.args, Load, 0) &&
            validate_keywords(exp->v.Call.keywords);
    case Num_kind: {
        PyObject *n = exp->v.Num.n;
        if (!PyLong_CheckExact(n) && !PyFloat_CheckExact(n) &&
            !PyComplex_CheckExact(n)) {
            PyErr_SetString(PyExc_TypeError, "non-numeric type in Num");
            return 0;
        }
        return 1;
    }
    case Str_kind: {
        PyObject *s = exp->v.Str.s;
        if (!PyUnicode_CheckExact(s)) {
            PyErr_SetString(PyExc_TypeError, "non-string type in Str");
            return 0;
        }
        return 1;
    }
    case JoinedStr_kind:
        return validate_exprs(exp->v.JoinedStr.values, Load, 0);
    case FormattedValue_kind:
        if (validate_expr(exp->v.FormattedValue.value, Load) == 0)
            return 0;
        if (exp->v.FormattedValue.format_spec)
            return validate_expr(exp->v.FormattedValue.format_spec, Load);
        return 1;
    case Bytes_kind: {
        PyObject *b = exp->v.Bytes.s;
        if (!PyBytes_CheckExact(b)) {
            PyErr_SetString(PyExc_TypeError, "non-bytes type in Bytes");
            return 0;
        }
        return 1;
    }
    case Attribute_kind:
        return validate_expr(exp->v.Attribute.value, Load);
    case Subscript_kind:
        return validate_slice(exp->v.Subscript.slice) &&
            validate_expr(exp->v.Subscript.value, Load);
    case Starred_kind:
        return validate_expr(exp->v.Starred.value, ctx);
    case List_kind:
        return validate_exprs(exp->v.List.elts, ctx, 0);
    case Tuple_kind:
        return validate_exprs(exp->v.Tuple.elts, ctx, 0);
    /* These last cases don't have any checking. */
    case Name_kind:
    case NameConstant_kind:
    case Ellipsis_kind:
        return 1;
    default:
        PyErr_SetString(PyExc_SystemError, "unexpected expression");
        return 0;
    }
}

static int
validate_nonempty_seq(asdl_seq *seq, const char *what, const char *owner)
{
    if (asdl_seq_LEN(seq))
        return 1;
    PyErr_Format(PyExc_ValueError, "empty %s on %s", what, owner);
    return 0;
}

static int
validate_assignlist(asdl_seq *targets, expr_context_ty ctx)
{
    return validate_nonempty_seq(targets, "targets", ctx == Del ? "Delete" : "Assign") &&
        validate_exprs(targets, ctx, 0);
}

static int
validate_body(asdl_seq *body, const char *owner)
{
    return validate_nonempty_seq(body, "body", owner) && validate_stmts(body);
}

static int
validate_stmt(stmt_ty stmt)
{
    int i;
    switch (stmt->kind) {
    case FunctionDef_kind:
        return validate_body(stmt->v.FunctionDef.body, "FunctionDef") &&
            validate_arguments(stmt->v.FunctionDef.args) &&
            validate_exprs(stmt->v.FunctionDef.decorator_list, Load, 0) &&
            (!stmt->v.FunctionDef.returns ||
             validate_expr(stmt->v.FunctionDef.returns, Load));
    case ClassDef_kind:
        return validate_body(stmt->v.ClassDef.body, "ClassDef") &&
            validate_exprs(stmt->v.ClassDef.bases, Load, 0) &&
            validate_keywords(stmt->v.ClassDef.keywords) &&
            validate_exprs(stmt->v.ClassDef.decorator_list, Load, 0);
    case Return_kind:
        return !stmt->v.Return.value || validate_expr(stmt->v.Return.value, Load);
    case Delete_kind:
        return validate_assignlist(stmt->v.Delete.targets, Del);
    case Assign_kind:
        return validate_assignlist(stmt->v.Assign.targets, Store) &&
            validate_expr(stmt->v.Assign.value, Load);
    case AugAssign_kind:
        return validate_expr(stmt->v.AugAssign.target, Store) &&
            validate_expr(stmt->v.AugAssign.value, Load);
    case For_kind:
        return validate_expr(stmt->v.For.target, Store) &&
            validate_expr(stmt->v.For.iter, Load) &&
            validate_body(stmt->v.For.body, "For") &&
            validate_stmts(stmt->v.For.orelse);
    case AsyncFor_kind:
        return validate_expr(stmt->v.AsyncFor.target, Store) &&
            validate_expr(stmt->v.AsyncFor.iter, Load) &&
            validate_body(stmt->v.AsyncFor.body, "AsyncFor") &&
            validate_stmts(stmt->v.AsyncFor.orelse);
    case While_kind:
        return validate_expr(stmt->v.While.test, Load) &&
            validate_body(stmt->v.While.body, "While") &&
            validate_stmts(stmt->v.While.orelse);
    case If_kind:
        return validate_expr(stmt->v.If.test, Load) &&
            validate_body(stmt->v.If.body, "If") &&
            validate_stmts(stmt->v.If.orelse);
    case With_kind:
        if (!validate_nonempty_seq(stmt->v.With.items, "items", "With"))
            return 0;
        for (i = 0; i < asdl_seq_LEN(stmt->v.With.items); i++) {
            withitem_ty item = asdl_seq_GET(stmt->v.With.items, i);
            if (!validate_expr(item->context_expr, Load) ||
                (item->optional_vars && !validate_expr(item->optional_vars, Store)))
                return 0;
        }
        return validate_body(stmt->v.With.body, "With");
    case AsyncWith_kind:
        if (!validate_nonempty_seq(stmt->v.AsyncWith.items, "items", "AsyncWith"))
            return 0;
        for (i = 0; i < asdl_seq_LEN(stmt->v.AsyncWith.items); i++) {
            withitem_ty item = asdl_seq_GET(stmt->v.AsyncWith.items, i);
            if (!validate_expr(item->context_expr, Load) ||
                (item->optional_vars && !validate_expr(item->optional_vars, Store)))
                return 0;
        }
        return validate_body(stmt->v.AsyncWith.body, "AsyncWith");
    case Raise_kind:
        if (stmt->v.Raise.exc) {
            return validate_expr(stmt->v.Raise.exc, Load) &&
                (!stmt->v.Raise.cause || validate_expr(stmt->v.Raise.cause, Load));
        }
        if (stmt->v.Raise.cause) {
            PyErr_SetString(PyExc_ValueError, "Raise with cause but no exception");
            return 0;
        }
        return 1;
    case Try_kind:
        if (!validate_body(stmt->v.Try.body, "Try"))
            return 0;
        if (!asdl_seq_LEN(stmt->v.Try.handlers) &&
            !asdl_seq_LEN(stmt->v.Try.finalbody)) {
            PyErr_SetString(PyExc_ValueError, "Try has neither except handlers nor finalbody");
            return 0;
        }
        if (!asdl_seq_LEN(stmt->v.Try.handlers) &&
            asdl_seq_LEN(stmt->v.Try.orelse)) {
            PyErr_SetString(PyExc_ValueError, "Try has orelse but no except handlers");
            return 0;
        }
        for (i = 0; i < asdl_seq_LEN(stmt->v.Try.handlers); i++) {
            excepthandler_ty handler = asdl_seq_GET(stmt->v.Try.handlers, i);
            if ((handler->v.ExceptHandler.type &&
                 !validate_expr(handler->v.ExceptHandler.type, Load)) ||
                !validate_body(handler->v.ExceptHandler.body, "ExceptHandler"))
                return 0;
        }
        return (!asdl_seq_LEN(stmt->v.Try.finalbody) ||
                validate_stmts(stmt->v.Try.finalbody)) &&
            (!asdl_seq_LEN(stmt->v.Try.orelse) ||
             validate_stmts(stmt->v.Try.orelse));
    case Assert_kind:
        return validate_expr(stmt->v.Assert.test, Load) &&
            (!stmt->v.Assert.msg || validate_expr(stmt->v.Assert.msg, Load));
    case Import_kind:
        return validate_nonempty_seq(stmt->v.Import.names, "names", "Import");
    case ImportFrom_kind:
        if (stmt->v.ImportFrom.level < -1) {
            PyErr_SetString(PyExc_ValueError, "ImportFrom level less than -1");
            return 0;
        }
        return validate_nonempty_seq(stmt->v.ImportFrom.names, "names", "ImportFrom");
    case Global_kind:
        return validate_nonempty_seq(stmt->v.Global.names, "names", "Global");
    case Nonlocal_kind:
        return validate_nonempty_seq(stmt->v.Nonlocal.names, "names", "Nonlocal");
    case Expr_kind:
        return validate_expr(stmt->v.Expr.value, Load);
    case AsyncFunctionDef_kind:
        return validate_body(stmt->v.AsyncFunctionDef.body, "AsyncFunctionDef") &&
            validate_arguments(stmt->v.AsyncFunctionDef.args) &&
            validate_exprs(stmt->v.AsyncFunctionDef.decorator_list, Load, 0) &&
            (!stmt->v.AsyncFunctionDef.returns ||
             validate_expr(stmt->v.AsyncFunctionDef.returns, Load));
    case Pass_kind:
    case Break_kind:
    case Continue_kind:
        return 1;
    default:
        PyErr_SetString(PyExc_SystemError, "unexpected statement");
        return 0;
    }
}

static int
validate_stmts(asdl_seq *seq)
{
    int i;
    for (i = 0; i < asdl_seq_LEN(seq); i++) {
        stmt_ty stmt = asdl_seq_GET(seq, i);
        if (stmt) {
            if (!validate_stmt(stmt))
                return 0;
        }
        else {
            PyErr_SetString(PyExc_ValueError,
                            "None disallowed in statement list");
            return 0;
        }
    }
    return 1;
}

static int
validate_exprs(asdl_seq *exprs, expr_context_ty ctx, int null_ok)
{
    int i;
    for (i = 0; i < asdl_seq_LEN(exprs); i++) {
        expr_ty expr = asdl_seq_GET(exprs, i);
        if (expr) {
            if (!validate_expr(expr, ctx))
                return 0;
        }
        else if (!null_ok) {
            PyErr_SetString(PyExc_ValueError,
                            "None disallowed in expression list");
            return 0;
        }

    }
    return 1;
}

int
PyAST_Validate(mod_ty mod)
{
    int res = 0;

    switch (mod->kind) {
    case Module_kind:
        res = validate_stmts(mod->v.Module.body);
        break;
    case Interactive_kind:
        res = validate_stmts(mod->v.Interactive.body);
        break;
    case Expression_kind:
        res = validate_expr(mod->v.Expression.body, Load);
        break;
    case Suite_kind:
        PyErr_SetString(PyExc_ValueError, "Suite is not valid in the CPython compiler");
        break;
    default:
        PyErr_SetString(PyExc_SystemError, "impossible module node");
        res = 0;
        break;
    }
    return res;
}

/* This is done here, so defines like "test" don't interfere with AST use above. */
#include "grammar.h"
#include "parsetok.h"
#include "graminit.h"

/* Data structure used internally */
struct compiling {
    char *c_encoding; /* source encoding */
    PyArena *c_arena; /* Arena for allocating memory. */
    PyObject *c_filename; /* filename */
    PyObject *c_normalize; /* Normalization function from unicodedata. */
    PyObject *c_normalize_args; /* Normalization argument tuple. */
};

static asdl_seq *seq_for_testlist(struct compiling *, const node *);
static expr_ty ast_for_expr(struct compiling *, const node *);
static stmt_ty ast_for_stmt(struct compiling *, const node *);
static asdl_seq *ast_for_suite(struct compiling *, const node *);
static asdl_seq *ast_for_exprlist(struct compiling *, const node *,
                                  expr_context_ty);
static expr_ty ast_for_testlist(struct compiling *, const node *);
static stmt_ty ast_for_classdef(struct compiling *, const node *, asdl_seq *);

static stmt_ty ast_for_with_stmt(struct compiling *, const node *, int);
static stmt_ty ast_for_for_stmt(struct compiling *, const node *, int);

/* Note different signature for ast_for_call */
static expr_ty ast_for_call(struct compiling *, const node *, expr_ty);

static PyObject *parsenumber(struct compiling *, const char *);
static expr_ty parsestrplus(struct compiling *, const node *n);

#define COMP_GENEXP   0
#define COMP_LISTCOMP 1
#define COMP_SETCOMP  2

static int
init_normalization(struct compiling *c)
{
    PyObject *m = PyImport_ImportModuleNoBlock("unicodedata");
    if (!m)
        return 0;
    c->c_normalize = PyObject_GetAttrString(m, "normalize");
    Py_DECREF(m);
    if (!c->c_normalize)
        return 0;
    c->c_normalize_args = Py_BuildValue("(sN)", "NFKC", Py_None);
    if (!c->c_normalize_args) {
        Py_CLEAR(c->c_normalize);
        return 0;
    }
    PyTuple_SET_ITEM(c->c_normalize_args, 1, NULL);
    return 1;
}

static identifier
new_identifier(const char *n, struct compiling *c)
{
    PyObject *id = PyUnicode_DecodeUTF8(n, strlen(n), NULL);
    if (!id)
        return NULL;
    /* PyUnicode_DecodeUTF8 should always return a ready string. */
    assert(PyUnicode_IS_READY(id));
    /* Check whether there are non-ASCII characters in the
       identifier; if so, normalize to NFKC. */
    if (!PyUnicode_IS_ASCII(id)) {
        PyObject *id2;
        if (!c->c_normalize && !init_normalization(c)) {
            Py_DECREF(id);
            return NULL;
        }
        PyTuple_SET_ITEM(c->c_normalize_args, 1, id);
        id2 = PyObject_Call(c->c_normalize, c->c_normalize_args, NULL);
        Py_DECREF(id);
        if (!id2)
            return NULL;
        id = id2;
    }
    PyUnicode_InternInPlace(&id);
    if (PyArena_AddPyObject(c->c_arena, id) < 0) {
        Py_DECREF(id);
        return NULL;
    }
    return id;
}

#define NEW_IDENTIFIER(n) new_identifier(STR(n), c)

static int
ast_error(struct compiling *c, const node *n, const char *errmsg)
{
    PyObject *value, *errstr, *loc, *tmp;

    loc = PyErr_ProgramTextObject(c->c_filename, LINENO(n));
    if (!loc) {
        Py_INCREF(Py_None);
        loc = Py_None;
    }
    tmp = Py_BuildValue("(OiiN)", c->c_filename, LINENO(n), n->n_col_offset, loc);
    if (!tmp)
        return 0;
    errstr = PyUnicode_FromString(errmsg);
    if (!errstr) {
        Py_DECREF(tmp);
        return 0;
    }
    value = PyTuple_Pack(2, errstr, tmp);
    Py_DECREF(errstr);
    Py_DECREF(tmp);
    if (value) {
        PyErr_SetObject(PyExc_SyntaxError, value);
        Py_DECREF(value);
    }
    return 0;
}

/* num_stmts() returns number of contained statements.

   Use this routine to determine how big a sequence is needed for
   the statements in a parse tree.  Its raison d'etre is this bit of
   grammar:

   stmt: simple_stmt | compound_stmt
   simple_stmt: small_stmt (';' small_stmt)* [';'] NEWLINE

   A simple_stmt can contain multiple small_stmt elements joined
   by semicolons.  If the arg is a simple_stmt, the number of
   small_stmt elements is returned.
*/

static int
num_stmts(const node *n)
{
    int i, l;
    node *ch;

    switch (TYPE(n)) {
        case single_input:
            if (TYPE(CHILD(n, 0)) == NEWLINE)
                return 0;
            else
                return num_stmts(CHILD(n, 0));
        case file_input:
            l = 0;
            for (i = 0; i < NCH(n); i++) {
                ch = CHILD(n, i);
                if (TYPE(ch) == stmt)
                    l += num_stmts(ch);
            }
            return l;
        case stmt:
            return num_stmts(CHILD(n, 0));
        case compound_stmt:
            return 1;
        case simple_stmt:
            return NCH(n) / 2; /* Divide by 2 to remove count of semi-colons */
        case suite:
            if (NCH(n) == 1)
                return num_stmts(CHILD(n, 0));
            else {
                l = 0;
                for (i = 2; i < (NCH(n) - 1); i++)
                    l += num_stmts(CHILD(n, i));
                return l;
            }
        default: {
            char buf[128];

            sprintf(buf, "Non-statement found: %d %d",
                    TYPE(n), NCH(n));
            Py_FatalError(buf);
        }
    }
    assert(0);
    return 0;
}

/* Transform the CST rooted at node * to the appropriate AST
*/

mod_ty
PyAST_FromNodeObject(const node *n, PyCompilerFlags *flags,
                     PyObject *filename, PyArena *arena)
{
    int i, j, k, num;
    asdl_seq *stmts = NULL;
    stmt_ty s;
    node *ch;
    struct compiling c;
    mod_ty res = NULL;

    c.c_arena = arena;
    /* borrowed reference */
    c.c_filename = filename;
    c.c_normalize = c.c_normalize_args = NULL;
    if (flags && flags->cf_flags & PyCF_SOURCE_IS_UTF8) {
        c.c_encoding = "utf-8";
        if (TYPE(n) == encoding_decl) {
#if 0
            ast_error(c, n, "encoding declaration in Unicode string");
            goto out;
#endif
            n = CHILD(n, 0);
        }
    } else if (TYPE(n) == encoding_decl) {
        c.c_encoding = STR(n);
        n = CHILD(n, 0);
    } else {
        /* PEP 3120 */
        c.c_encoding = "utf-8";
    }

    k = 0;
    switch (TYPE(n)) {
        case file_input:
            stmts = _Py_asdl_seq_new(num_stmts(n), arena);
            if (!stmts)
                goto out;
            for (i = 0; i < NCH(n) - 1; i++) {
                ch = CHILD(n, i);
                if (TYPE(ch) == NEWLINE)
                    continue;
                REQ(ch, stmt);
                num = num_stmts(ch);
                if (num == 1) {
                    s = ast_for_stmt(&c, ch);
                    if (!s)
                        goto out;
                    asdl_seq_SET(stmts, k++, s);
                }
                else {
                    ch = CHILD(ch, 0);
                    REQ(ch, simple_stmt);
                    for (j = 0; j < num; j++) {
                        s = ast_for_stmt(&c, CHILD(ch, j * 2));
                        if (!s)
                            goto out;
                        asdl_seq_SET(stmts, k++, s);
                    }
                }
            }
            res = Module(stmts, arena);
            break;
        case eval_input: {
            expr_ty testlist_ast;

            /* XXX Why not comp_for here? */
            testlist_ast = ast_for_testlist(&c, CHILD(n, 0));
            if (!testlist_ast)
                goto out;
            res = Expression(testlist_ast, arena);
            break;
        }
        case single_input:
            if (TYPE(CHILD(n, 0)) == NEWLINE) {
                stmts = _Py_asdl_seq_new(1, arena);
                if (!stmts)
                    goto out;
                asdl_seq_SET(stmts, 0, Pass(n->n_lineno, n->n_col_offset,
                                            arena));
                if (!asdl_seq_GET(stmts, 0))
                    goto out;
                res = Interactive(stmts, arena);
            }
            else {
                n = CHILD(n, 0);
                num = num_stmts(n);
                stmts = _Py_asdl_seq_new(num, arena);
                if (!stmts)
                    goto out;
                if (num == 1) {
                    s = ast_for_stmt(&c, n);
                    if (!s)
                        goto out;
                    asdl_seq_SET(stmts, 0, s);
                }
                else {
                    /* Only a simple_stmt can contain multiple statements. */
                    REQ(n, simple_stmt);
                    for (i = 0; i < NCH(n); i += 2) {
                        if (TYPE(CHILD(n, i)) == NEWLINE)
                            break;
                        s = ast_for_stmt(&c, CHILD(n, i));
                        if (!s)
                            goto out;
                        asdl_seq_SET(stmts, i / 2, s);
                    }
                }

                res = Interactive(stmts, arena);
            }
            break;
        default:
            PyErr_Format(PyExc_SystemError,
                         "invalid node %d for PyAST_FromNode", TYPE(n));
            goto out;
    }
 out:
    if (c.c_normalize) {
        Py_DECREF(c.c_normalize);
        PyTuple_SET_ITEM(c.c_normalize_args, 1, NULL);
        Py_DECREF(c.c_normalize_args);
    }
    return res;
}

mod_ty
PyAST_FromNode(const node *n, PyCompilerFlags *flags, const char *filename_str,
               PyArena *arena)
{
    mod_ty mod;
    PyObject *filename;
    filename = PyUnicode_DecodeFSDefault(filename_str);
    if (filename == NULL)
        return NULL;
    mod = PyAST_FromNodeObject(n, flags, filename, arena);
    Py_DECREF(filename);
    return mod;

}

/* Return the AST repr. of the operator represented as syntax (|, ^, etc.)
*/

static operator_ty
get_operator(const node *n)
{
    switch (TYPE(n)) {
        case VBAR:
            return BitOr;
        case CIRCUMFLEX:
            return BitXor;
        case AMPER:
            return BitAnd;
        case LEFTSHIFT:
            return LShift;
        case RIGHTSHIFT:
            return RShift;
        case PLUS:
            return Add;
        case MINUS:
            return Sub;
        case STAR:
            return Mult;
        case AT:
            return MatMult;
        case SLASH:
            return Div;
        case DOUBLESLASH:
            return FloorDiv;
        case PERCENT:
            return Mod;
        default:
            return (operator_ty)0;
    }
}

static const char* FORBIDDEN[] = {
    "None",
    "True",
    "False",
    NULL,
};

static int
forbidden_name(struct compiling *c, identifier name, const node *n,
               int full_checks)
{
    assert(PyUnicode_Check(name));
    if (PyUnicode_CompareWithASCIIString(name, "__debug__") == 0) {
        ast_error(c, n, "assignment to keyword");
        return 1;
    }
    if (full_checks) {
        const char **p;
        for (p = FORBIDDEN; *p; p++) {
            if (PyUnicode_CompareWithASCIIString(name, *p) == 0) {
                ast_error(c, n, "assignment to keyword");
                return 1;
            }
        }
    }
    return 0;
}

/* Set the context ctx for expr_ty e, recursively traversing e.

   Only sets context for expr kinds that "can appear in assignment context"
   (according to ../Parser/Python.asdl).  For other expr kinds, it sets
   an appropriate syntax error and returns false.
*/

static int
set_context(struct compiling *c, expr_ty e, expr_context_ty ctx, const node *n)
{
    asdl_seq *s = NULL;
    /* If a particular expression type can't be used for assign / delete,
       set expr_name to its name and an error message will be generated.
    */
    const char* expr_name = NULL;

    /* The ast defines augmented store and load contexts, but the
       implementation here doesn't actually use them.  The code may be
       a little more complex than necessary as a result.  It also means
       that expressions in an augmented assignment have a Store context.
       Consider restructuring so that augmented assignment uses
       set_context(), too.
    */
    assert(ctx != AugStore && ctx != AugLoad);

    switch (e->kind) {
        case Attribute_kind:
            e->v.Attribute.ctx = ctx;
            if (ctx == Store && forbidden_name(c, e->v.Attribute.attr, n, 1))
                return 0;
            break;
        case Subscript_kind:
            e->v.Subscript.ctx = ctx;
            break;
        case Starred_kind:
            e->v.Starred.ctx = ctx;
            if (!set_context(c, e->v.Starred.value, ctx, n))
                return 0;
            break;
        case Name_kind:
            if (ctx == Store) {
                if (forbidden_name(c, e->v.Name.id, n, 0))
                    return 0; /* forbidden_name() calls ast_error() */
            }
            e->v.Name.ctx = ctx;
            break;
        case List_kind:
            e->v.List.ctx = ctx;
            s = e->v.List.elts;
            break;
        case Tuple_kind:
            if (asdl_seq_LEN(e->v.Tuple.elts))  {
                e->v.Tuple.ctx = ctx;
                s = e->v.Tuple.elts;
            }
            else {
                expr_name = "()";
            }
            break;
        case Lambda_kind:
            expr_name = "lambda";
            break;
        case Call_kind:
            expr_name = "function call";
            break;
        case BoolOp_kind:
        case BinOp_kind:
        case UnaryOp_kind:
            expr_name = "operator";
            break;
        case GeneratorExp_kind:
            expr_name = "generator expression";
            break;
        case Yield_kind:
        case YieldFrom_kind:
            expr_name = "yield expression";
            break;
        case Await_kind:
            expr_name = "await expression";
            break;
        case ListComp_kind:
            expr_name = "list comprehension";
            break;
        case SetComp_kind:
            expr_name = "set comprehension";
            break;
        case DictComp_kind:
            expr_name = "dict comprehension";
            break;
        case Dict_kind:
        case Set_kind:
        case Num_kind:
        case Str_kind:
        case Bytes_kind:
        case JoinedStr_kind:
        case FormattedValue_kind:
            expr_name = "literal";
            break;
        case NameConstant_kind:
            expr_name = "keyword";
            break;
        case Ellipsis_kind:
            expr_name = "Ellipsis";
            break;
        case Compare_kind:
            expr_name = "comparison";
            break;
        case IfExp_kind:
            expr_name = "conditional expression";
            break;
        default:
            PyErr_Format(PyExc_SystemError,
                         "unexpected expression in assignment %d (line %d)",
                         e->kind, e->lineno);
            return 0;
    }
    /* Check for error string set by switch */
    if (expr_name) {
        char buf[300];
        PyOS_snprintf(buf, sizeof(buf),
                      "can't %s %s",
                      ctx == Store ? "assign to" : "delete",
                      expr_name);
        return ast_error(c, n, buf);
    }

    /* If the LHS is a list or tuple, we need to set the assignment
       context for all the contained elements.
    */
    if (s) {
        int i;

        for (i = 0; i < asdl_seq_LEN(s); i++) {
            if (!set_context(c, (expr_ty)asdl_seq_GET(s, i), ctx, n))
                return 0;
        }
    }
    return 1;
}

static operator_ty
ast_for_augassign(struct compiling *c, const node *n)
{
    REQ(n, augassign);
    n = CHILD(n, 0);
    switch (STR(n)[0]) {
        case '+':
            return Add;
        case '-':
            return Sub;
        case '/':
            if (STR(n)[1] == '/')
                return FloorDiv;
            else
                return Div;
        case '%':
            return Mod;
        case '<':
            return LShift;
        case '>':
            return RShift;
        case '&':
            return BitAnd;
        case '^':
            return BitXor;
        case '|':
            return BitOr;
        case '*':
            if (STR(n)[1] == '*')
                return Pow;
            else
                return Mult;
        case '@':
            return MatMult;
        default:
            PyErr_Format(PyExc_SystemError, "invalid augassign: %s", STR(n));
            return (operator_ty)0;
    }
}

static cmpop_ty
ast_for_comp_op(struct compiling *c, const node *n)
{
    /* comp_op: '<'|'>'|'=='|'>='|'<='|'!='|'in'|'not' 'in'|'is'
               |'is' 'not'
    */
    REQ(n, comp_op);
    if (NCH(n) == 1) {
        n = CHILD(n, 0);
        switch (TYPE(n)) {
            case LESS:
                return Lt;
            case GREATER:
                return Gt;
            case EQEQUAL:                       /* == */
                return Eq;
            case LESSEQUAL:
                return LtE;
            case GREATEREQUAL:
                return GtE;
            case NOTEQUAL:
                return NotEq;
            case NAME:
                if (strcmp(STR(n), "in") == 0)
                    return In;
                if (strcmp(STR(n), "is") == 0)
                    return Is;
            default:
                PyErr_Format(PyExc_SystemError, "invalid comp_op: %s",
                             STR(n));
                return (cmpop_ty)0;
        }
    }
    else if (NCH(n) == 2) {
        /* handle "not in" and "is not" */
        switch (TYPE(CHILD(n, 0))) {
            case NAME:
                if (strcmp(STR(CHILD(n, 1)), "in") == 0)
                    return NotIn;
                if (strcmp(STR(CHILD(n, 0)), "is") == 0)
                    return IsNot;
            default:
                PyErr_Format(PyExc_SystemError, "invalid comp_op: %s %s",
                             STR(CHILD(n, 0)), STR(CHILD(n, 1)));
                return (cmpop_ty)0;
        }
    }
    PyErr_Format(PyExc_SystemError, "invalid comp_op: has %d children",
                 NCH(n));
    return (cmpop_ty)0;
}

static asdl_seq *
seq_for_testlist(struct compiling *c, const node *n)
{
    /* testlist: test (',' test)* [',']
       testlist_star_expr: test|star_expr (',' test|star_expr)* [',']
    */
    asdl_seq *seq;
    expr_ty expression;
    int i;
    assert(TYPE(n) == testlist || TYPE(n) == testlist_star_expr || TYPE(n) == testlist_comp);

    seq = _Py_asdl_seq_new((NCH(n) + 1) / 2, c->c_arena);
    if (!seq)
        return NULL;

    for (i = 0; i < NCH(n); i += 2) {
        const node *ch = CHILD(n, i);
        assert(TYPE(ch) == test || TYPE(ch) == test_nocond || TYPE(ch) == star_expr);

        expression = ast_for_expr(c, ch);
        if (!expression)
            return NULL;

        assert(i / 2 < seq->size);
        asdl_seq_SET(seq, i / 2, expression);
    }
    return seq;
}

static arg_ty
ast_for_arg(struct compiling *c, const node *n)
{
    identifier name;
    expr_ty annotation = NULL;
    node *ch;
    arg_ty ret;

    assert(TYPE(n) == tfpdef || TYPE(n) == vfpdef);
    ch = CHILD(n, 0);
    name = NEW_IDENTIFIER(ch);
    if (!name)
        return NULL;
    if (forbidden_name(c, name, ch, 0))
        return NULL;

    if (NCH(n) == 3 && TYPE(CHILD(n, 1)) == COLON) {
        annotation = ast_for_expr(c, CHILD(n, 2));
        if (!annotation)
            return NULL;
    }

    ret = arg(name, annotation, c->c_arena);
    if (!ret)
        return NULL;
    ret->lineno = LINENO(n);
    ret->col_offset = n->n_col_offset;
    return ret;
}

/* returns -1 if failed to handle keyword only arguments
   returns new position to keep processing if successful
               (',' tfpdef ['=' test])*
                     ^^^
   start pointing here
 */
static int
handle_keywordonly_args(struct compiling *c, const node *n, int start,
                        asdl_seq *kwonlyargs, asdl_seq *kwdefaults)
{
    PyObject *argname;
    node *ch;
    expr_ty expression, annotation;
    arg_ty arg;
    int i = start;
    int j = 0; /* index for kwdefaults and kwonlyargs */

    if (kwonlyargs == NULL) {
        ast_error(c, CHILD(n, start), "named arguments must follow bare *");
        return -1;
    }
    assert(kwdefaults != NULL);
    while (i < NCH(n)) {
        ch = CHILD(n, i);
        switch (TYPE(ch)) {
            case vfpdef:
            case tfpdef:
                if (i + 1 < NCH(n) && TYPE(CHILD(n, i + 1)) == EQUAL) {
                    expression = ast_for_expr(c, CHILD(n, i + 2));
                    if (!expression)
                        goto error;
                    asdl_seq_SET(kwdefaults, j, expression);
                    i += 2; /* '=' and test */
                }
                else { /* setting NULL if no default value exists */
                    asdl_seq_SET(kwdefaults, j, NULL);
                }
                if (NCH(ch) == 3) {
                    /* ch is NAME ':' test */
                    annotation = ast_for_expr(c, CHILD(ch, 2));
                    if (!annotation)
                        goto error;
                }
                else {
                    annotation = NULL;
                }
                ch = CHILD(ch, 0);
                argname = NEW_IDENTIFIER(ch);
                if (!argname)
                    goto error;
                if (forbidden_name(c, argname, ch, 0))
                    goto error;
                arg = arg(argname, annotation, c->c_arena);
                if (!arg)
                    goto error;
                arg->lineno = LINENO(ch);
                arg->col_offset = ch->n_col_offset;
                asdl_seq_SET(kwonlyargs, j++, arg);
                i += 2; /* the name and the comma */
                break;
            case DOUBLESTAR:
                return i;
            default:
                ast_error(c, ch, "unexpected node");
                goto error;
        }
    }
    return i;
 error:
    return -1;
}

/* Create AST for argument list. */

static arguments_ty
ast_for_arguments(struct compiling *c, const node *n)
{
    /* This function handles both typedargslist (function definition)
       and varargslist (lambda definition).

       parameters: '(' [typedargslist] ')'
       typedargslist: (tfpdef ['=' test] (',' tfpdef ['=' test])* [',' [
               '*' [tfpdef] (',' tfpdef ['=' test])* [',' ['**' tfpdef [',']]]
             | '**' tfpdef [',']]]
         | '*' [tfpdef] (',' tfpdef ['=' test])* [',' ['**' tfpdef [',']]]
         | '**' tfpdef [','])
       tfpdef: NAME [':' test]
       varargslist: (vfpdef ['=' test] (',' vfpdef ['=' test])* [',' [
               '*' [vfpdef] (',' vfpdef ['=' test])* [',' ['**' vfpdef [',']]]
             | '**' vfpdef [',']]]
         | '*' [vfpdef] (',' vfpdef ['=' test])* [',' ['**' vfpdef [',']]]
         | '**' vfpdef [',']
       )
       vfpdef: NAME

    */
    int i, j, k, nposargs = 0, nkwonlyargs = 0;
    int nposdefaults = 0, found_default = 0;
    asdl_seq *posargs, *posdefaults, *kwonlyargs, *kwdefaults;
    arg_ty vararg = NULL, kwarg = NULL;
    arg_ty arg;
    node *ch;

    if (TYPE(n) == parameters) {
        if (NCH(n) == 2) /* () as argument list */
            return arguments(NULL, NULL, NULL, NULL, NULL, NULL, c->c_arena);
        n = CHILD(n, 1);
    }
    assert(TYPE(n) == typedargslist || TYPE(n) == varargslist);

    /* First count the number of positional args & defaults.  The
       variable i is the loop index for this for loop and the next.
       The next loop picks up where the first leaves off.
    */
    for (i = 0; i < NCH(n); i++) {
        ch = CHILD(n, i);
        if (TYPE(ch) == STAR) {
            /* skip star */
            i++;
            if (i < NCH(n) && /* skip argument following star */
                (TYPE(CHILD(n, i)) == tfpdef ||
                 TYPE(CHILD(n, i)) == vfpdef)) {
                i++;
            }
            break;
        }
        if (TYPE(ch) == DOUBLESTAR) break;
        if (TYPE(ch) == vfpdef || TYPE(ch) == tfpdef) nposargs++;
        if (TYPE(ch) == EQUAL) nposdefaults++;
    }
    /* count the number of keyword only args &
       defaults for keyword only args */
    for ( ; i < NCH(n); ++i) {
        ch = CHILD(n, i);
        if (TYPE(ch) == DOUBLESTAR) break;
        if (TYPE(ch) == tfpdef || TYPE(ch) == vfpdef) nkwonlyargs++;
    }
    posargs = (nposargs ? _Py_asdl_seq_new(nposargs, c->c_arena) : NULL);
    if (!posargs && nposargs)
        return NULL;
    kwonlyargs = (nkwonlyargs ?
                   _Py_asdl_seq_new(nkwonlyargs, c->c_arena) : NULL);
    if (!kwonlyargs && nkwonlyargs)
        return NULL;
    posdefaults = (nposdefaults ?
                    _Py_asdl_seq_new(nposdefaults, c->c_arena) : NULL);
    if (!posdefaults && nposdefaults)
        return NULL;
    /* The length of kwonlyargs and kwdefaults are same
       since we set NULL as default for keyword only argument w/o default
       - we have sequence data structure, but no dictionary */
    kwdefaults = (nkwonlyargs ?
                   _Py_asdl_seq_new(nkwonlyargs, c->c_arena) : NULL);
    if (!kwdefaults && nkwonlyargs)
        return NULL;

    if (nposargs + nkwonlyargs > 255) {
        ast_error(c, n, "more than 255 arguments");
        return NULL;
    }

    /* tfpdef: NAME [':' test]
       vfpdef: NAME
    */
    i = 0;
    j = 0;  /* index for defaults */
    k = 0;  /* index for args */
    while (i < NCH(n)) {
        ch = CHILD(n, i);
        switch (TYPE(ch)) {
            case tfpdef:
            case vfpdef:
                /* XXX Need to worry about checking if TYPE(CHILD(n, i+1)) is
                   anything other than EQUAL or a comma? */
                /* XXX Should NCH(n) check be made a separate check? */
                if (i + 1 < NCH(n) && TYPE(CHILD(n, i + 1)) == EQUAL) {
                    expr_ty expression = ast_for_expr(c, CHILD(n, i + 2));
                    if (!expression)
                        return NULL;
                    assert(posdefaults != NULL);
                    asdl_seq_SET(posdefaults, j++, expression);
                    i += 2;
                    found_default = 1;
                }
                else if (found_default) {
                    ast_error(c, n,
                             "non-default argument follows default argument");
                    return NULL;
                }
                arg = ast_for_arg(c, ch);
                if (!arg)
                    return NULL;
                asdl_seq_SET(posargs, k++, arg);
                i += 2; /* the name and the comma */
                break;
            case STAR:
                if (i+1 >= NCH(n) ||
                    (i+2 == NCH(n) && TYPE(CHILD(n, i+1)) == COMMA)) {
                    ast_error(c, CHILD(n, i),
                        "named arguments must follow bare *");
                    return NULL;
                }
                ch = CHILD(n, i+1);  /* tfpdef or COMMA */
                if (TYPE(ch) == COMMA) {
                    int res = 0;
                    i += 2; /* now follows keyword only arguments */
                    res = handle_keywordonly_args(c, n, i,
                                                  kwonlyargs, kwdefaults);
                    if (res == -1) return NULL;
                    i = res; /* res has new position to process */
                }
                else {
                    vararg = ast_for_arg(c, ch);
                    if (!vararg)
                        return NULL;

                    i += 3;
                    if (i < NCH(n) && (TYPE(CHILD(n, i)) == tfpdef
                                    || TYPE(CHILD(n, i)) == vfpdef)) {
                        int res = 0;
                        res = handle_keywordonly_args(c, n, i,
                                                      kwonlyargs, kwdefaults);
                        if (res == -1) return NULL;
                        i = res; /* res has new position to process */
                    }
                }
                break;
            case DOUBLESTAR:
                ch = CHILD(n, i+1);  /* tfpdef */
                assert(TYPE(ch) == tfpdef || TYPE(ch) == vfpdef);
                kwarg = ast_for_arg(c, ch);
                if (!kwarg)
                    return NULL;
                i += 3;
                break;
            default:
                PyErr_Format(PyExc_SystemError,
                             "unexpected node in varargslist: %d @ %d",
                             TYPE(ch), i);
                return NULL;
        }
    }
    return arguments(posargs, vararg, kwonlyargs, kwdefaults, kwarg, posdefaults, c->c_arena);
}

static expr_ty
ast_for_dotted_name(struct compiling *c, const node *n)
{
    expr_ty e;
    identifier id;
    int lineno, col_offset;
    int i;

    REQ(n, dotted_name);

    lineno = LINENO(n);
    col_offset = n->n_col_offset;

    id = NEW_IDENTIFIER(CHILD(n, 0));
    if (!id)
        return NULL;
    e = Name(id, Load, lineno, col_offset, c->c_arena);
    if (!e)
        return NULL;

    for (i = 2; i < NCH(n); i+=2) {
        id = NEW_IDENTIFIER(CHILD(n, i));
        if (!id)
            return NULL;
        e = Attribute(e, id, Load, lineno, col_offset, c->c_arena);
        if (!e)
            return NULL;
    }

    return e;
}

static expr_ty
ast_for_decorator(struct compiling *c, const node *n)
{
    /* decorator: '@' dotted_name [ '(' [arglist] ')' ] NEWLINE */
    expr_ty d = NULL;
    expr_ty name_expr;

    REQ(n, decorator);
    REQ(CHILD(n, 0), AT);
    REQ(RCHILD(n, -1), NEWLINE);

    name_expr = ast_for_dotted_name(c, CHILD(n, 1));
    if (!name_expr)
        return NULL;

    if (NCH(n) == 3) { /* No arguments */
        d = name_expr;
        name_expr = NULL;
    }
    else if (NCH(n) == 5) { /* Call with no arguments */
        d = Call(name_expr, NULL, NULL, LINENO(n),
                 n->n_col_offset, c->c_arena);
        if (!d)
            return NULL;
        name_expr = NULL;
    }
    else {
        d = ast_for_call(c, CHILD(n, 3), name_expr);
        if (!d)
            return NULL;
        name_expr = NULL;
    }

    return d;
}

static asdl_seq*
ast_for_decorators(struct compiling *c, const node *n)
{
    asdl_seq* decorator_seq;
    expr_ty d;
    int i;

    REQ(n, decorators);
    decorator_seq = _Py_asdl_seq_new(NCH(n), c->c_arena);
    if (!decorator_seq)
        return NULL;

    for (i = 0; i < NCH(n); i++) {
        d = ast_for_decorator(c, CHILD(n, i));
        if (!d)
            return NULL;
        asdl_seq_SET(decorator_seq, i, d);
    }
    return decorator_seq;
}

static stmt_ty
ast_for_funcdef_impl(struct compiling *c, const node *n,
                     asdl_seq *decorator_seq, int is_async)
{
    /* funcdef: 'def' NAME parameters ['->' test] ':' suite */
    identifier name;
    arguments_ty args;
    asdl_seq *body;
    expr_ty returns = NULL;
    int name_i = 1;

    REQ(n, funcdef);

    name = NEW_IDENTIFIER(CHILD(n, name_i));
    if (!name)
        return NULL;
    if (forbidden_name(c, name, CHILD(n, name_i), 0))
        return NULL;
    args = ast_for_arguments(c, CHILD(n, name_i + 1));
    if (!args)
        return NULL;
    if (TYPE(CHILD(n, name_i+2)) == RARROW) {
        returns = ast_for_expr(c, CHILD(n, name_i + 3));
        if (!returns)
            return NULL;
        name_i += 2;
    }
    body = ast_for_suite(c, CHILD(n, name_i + 3));
    if (!body)
        return NULL;

    if (is_async)
        return AsyncFunctionDef(name, args, body, decorator_seq, returns,
                                LINENO(n),
                                n->n_col_offset, c->c_arena);
    else
        return FunctionDef(name, args, body, decorator_seq, returns,
                           LINENO(n),
                           n->n_col_offset, c->c_arena);
}

static stmt_ty
ast_for_async_funcdef(struct compiling *c, const node *n, asdl_seq *decorator_seq)
{
    /* async_funcdef: ASYNC funcdef */
    REQ(n, async_funcdef);
    REQ(CHILD(n, 0), ASYNC);
    REQ(CHILD(n, 1), funcdef);

    return ast_for_funcdef_impl(c, CHILD(n, 1), decorator_seq,
                                1 /* is_async */);
}

static stmt_ty
ast_for_funcdef(struct compiling *c, const node *n, asdl_seq *decorator_seq)
{
    /* funcdef: 'def' NAME parameters ['->' test] ':' suite */
    return ast_for_funcdef_impl(c, n, decorator_seq,
                                0 /* is_async */);
}


static stmt_ty
ast_for_async_stmt(struct compiling *c, const node *n)
{
    /* async_stmt: ASYNC (funcdef | with_stmt | for_stmt) */
    REQ(n, async_stmt);
    REQ(CHILD(n, 0), ASYNC);

    switch (TYPE(CHILD(n, 1))) {
        case funcdef:
            return ast_for_funcdef_impl(c, CHILD(n, 1), NULL,
                                        1 /* is_async */);
        case with_stmt:
            return ast_for_with_stmt(c, CHILD(n, 1),
                                     1 /* is_async */);

        case for_stmt:
            return ast_for_for_stmt(c, CHILD(n, 1),
                                    1 /* is_async */);

        default:
            PyErr_Format(PyExc_SystemError,
                         "invalid async stament: %s",
                         STR(CHILD(n, 1)));
            return NULL;
    }
}

static stmt_ty
ast_for_decorated(struct compiling *c, const node *n)
{
    /* decorated: decorators (classdef | funcdef | async_funcdef) */
    stmt_ty thing = NULL;
    asdl_seq *decorator_seq = NULL;

    REQ(n, decorated);

    decorator_seq = ast_for_decorators(c, CHILD(n, 0));
    if (!decorator_seq)
      return NULL;

    assert(TYPE(CHILD(n, 1)) == funcdef ||
           TYPE(CHILD(n, 1)) == async_funcdef ||
           TYPE(CHILD(n, 1)) == classdef);

    if (TYPE(CHILD(n, 1)) == funcdef) {
      thing = ast_for_funcdef(c, CHILD(n, 1), decorator_seq);
    } else if (TYPE(CHILD(n, 1)) == classdef) {
      thing = ast_for_classdef(c, CHILD(n, 1), decorator_seq);
    } else if (TYPE(CHILD(n, 1)) == async_funcdef) {
      thing = ast_for_async_funcdef(c, CHILD(n, 1), decorator_seq);
    }
    /* we count the decorators in when talking about the class' or
     * function's line number */
    if (thing) {
        thing->lineno = LINENO(n);
        thing->col_offset = n->n_col_offset;
    }
    return thing;
}

static expr_ty
ast_for_lambdef(struct compiling *c, const node *n)
{
    /* lambdef: 'lambda' [varargslist] ':' test
       lambdef_nocond: 'lambda' [varargslist] ':' test_nocond */
    arguments_ty args;
    expr_ty expression;

    if (NCH(n) == 3) {
        args = arguments(NULL, NULL, NULL, NULL, NULL, NULL, c->c_arena);
        if (!args)
            return NULL;
        expression = ast_for_expr(c, CHILD(n, 2));
        if (!expression)
            return NULL;
    }
    else {
        args = ast_for_arguments(c, CHILD(n, 1));
        if (!args)
            return NULL;
        expression = ast_for_expr(c, CHILD(n, 3));
        if (!expression)
            return NULL;
    }

    return Lambda(args, expression, LINENO(n), n->n_col_offset, c->c_arena);
}

static expr_ty
ast_for_ifexpr(struct compiling *c, const node *n)
{
    /* test: or_test 'if' or_test 'else' test */
    expr_ty expression, body, orelse;

    assert(NCH(n) == 5);
    body = ast_for_expr(c, CHILD(n, 0));
    if (!body)
        return NULL;
    expression = ast_for_expr(c, CHILD(n, 2));
    if (!expression)
        return NULL;
    orelse = ast_for_expr(c, CHILD(n, 4));
    if (!orelse)
        return NULL;
    return IfExp(expression, body, orelse, LINENO(n), n->n_col_offset,
                 c->c_arena);
}

/*
   Count the number of 'for' loops in a comprehension.

   Helper for ast_for_comprehension().
*/

static int
count_comp_fors(struct compiling *c, const node *n)
{
    int n_fors = 0;

  count_comp_for:
    n_fors++;
    REQ(n, comp_for);
    if (NCH(n) == 5)
        n = CHILD(n, 4);
    else
        return n_fors;
  count_comp_iter:
    REQ(n, comp_iter);
    n = CHILD(n, 0);
    if (TYPE(n) == comp_for)
        goto count_comp_for;
    else if (TYPE(n) == comp_if) {
        if (NCH(n) == 3) {
            n = CHILD(n, 2);
            goto count_comp_iter;
        }
        else
            return n_fors;
    }

    /* Should never be reached */
    PyErr_SetString(PyExc_SystemError,
                    "logic error in count_comp_fors");
    return -1;
}

/* Count the number of 'if' statements in a comprehension.

   Helper for ast_for_comprehension().
*/

static int
count_comp_ifs(struct compiling *c, const node *n)
{
    int n_ifs = 0;

    while (1) {
        REQ(n, comp_iter);
        if (TYPE(CHILD(n, 0)) == comp_for)
            return n_ifs;
        n = CHILD(n, 0);
        REQ(n, comp_if);
        n_ifs++;
        if (NCH(n) == 2)
            return n_ifs;
        n = CHILD(n, 2);
    }
}

static asdl_seq *
ast_for_comprehension(struct compiling *c, const node *n)
{
    int i, n_fors;
    asdl_seq *comps;

    n_fors = count_comp_fors(c, n);
    if (n_fors == -1)
        return NULL;

    comps = _Py_asdl_seq_new(n_fors, c->c_arena);
    if (!comps)
        return NULL;

    for (i = 0; i < n_fors; i++) {
        comprehension_ty comp;
        asdl_seq *t;
        expr_ty expression, first;
        node *for_ch;

        REQ(n, comp_for);

        for_ch = CHILD(n, 1);
        t = ast_for_exprlist(c, for_ch, Store);
        if (!t)
            return NULL;
        expression = ast_for_expr(c, CHILD(n, 3));
        if (!expression)
            return NULL;

        /* Check the # of children rather than the length of t, since
           (x for x, in ...) has 1 element in t, but still requires a Tuple. */
        first = (expr_ty)asdl_seq_GET(t, 0);
        if (NCH(for_ch) == 1)
            comp = comprehension(first, expression, NULL, c->c_arena);
        else
            comp = comprehension(Tuple(t, Store, first->lineno, first->col_offset,
                                     c->c_arena),
                               expression, NULL, c->c_arena);
        if (!comp)
            return NULL;

        if (NCH(n) == 5) {
            int j, n_ifs;
            asdl_seq *ifs;

            n = CHILD(n, 4);
            n_ifs = count_comp_ifs(c, n);
            if (n_ifs == -1)
                return NULL;

            ifs = _Py_asdl_seq_new(n_ifs, c->c_arena);
            if (!ifs)
                return NULL;

            for (j = 0; j < n_ifs; j++) {
                REQ(n, comp_iter);
                n = CHILD(n, 0);
                REQ(n, comp_if);

                expression = ast_for_expr(c, CHILD(n, 1));
                if (!expression)
                    return NULL;
                asdl_seq_SET(ifs, j, expression);
                if (NCH(n) == 3)
                    n = CHILD(n, 2);
            }
            /* on exit, must guarantee that n is a comp_for */
            if (TYPE(n) == comp_iter)
                n = CHILD(n, 0);
            comp->ifs = ifs;
        }
        asdl_seq_SET(comps, i, comp);
    }
    return comps;
}

static expr_ty
ast_for_itercomp(struct compiling *c, const node *n, int type)
{
    /* testlist_comp: (test|star_expr)
     *                ( comp_for | (',' (test|star_expr))* [','] ) */
    expr_ty elt;
    asdl_seq *comps;
    node *ch;

    assert(NCH(n) > 1);

    ch = CHILD(n, 0);
    elt = ast_for_expr(c, ch);
    if (!elt)
        return NULL;
    if (elt->kind == Starred_kind) {
        ast_error(c, ch, "iterable unpacking cannot be used in comprehension");
        return NULL;
    }

    comps = ast_for_comprehension(c, CHILD(n, 1));
    if (!comps)
        return NULL;

    if (type == COMP_GENEXP)
        return GeneratorExp(elt, comps, LINENO(n), n->n_col_offset, c->c_arena);
    else if (type == COMP_LISTCOMP)
        return ListComp(elt, comps, LINENO(n), n->n_col_offset, c->c_arena);
    else if (type == COMP_SETCOMP)
        return SetComp(elt, comps, LINENO(n), n->n_col_offset, c->c_arena);
    else
        /* Should never happen */
        return NULL;
}

/* Fills in the key, value pair corresponding to the dict element.  In case
 * of an unpacking, key is NULL.  *i is advanced by the number of ast
 * elements.  Iff successful, nonzero is returned.
 */
static int
ast_for_dictelement(struct compiling *c, const node *n, int *i,
                    expr_ty *key, expr_ty *value)
{
    expr_ty expression;
    if (TYPE(CHILD(n, *i)) == DOUBLESTAR) {
        assert(NCH(n) - *i >= 2);

        expression = ast_for_expr(c, CHILD(n, *i + 1));
        if (!expression)
            return 0;
        *key = NULL;
        *value = expression;

        *i += 2;
    }
    else {
        assert(NCH(n) - *i >= 3);

        expression = ast_for_expr(c, CHILD(n, *i));
        if (!expression)
            return 0;
        *key = expression;

        REQ(CHILD(n, *i + 1), COLON);

        expression = ast_for_expr(c, CHILD(n, *i + 2));
        if (!expression)
            return 0;
        *value = expression;

        *i += 3;
    }
    return 1;
}

static expr_ty
ast_for_dictcomp(struct compiling *c, const node *n)
{
    expr_ty key, value;
    asdl_seq *comps;
    int i = 0;

    if (!ast_for_dictelement(c, n, &i, &key, &value))
        return NULL;
    assert(key);
    assert(NCH(n) - i >= 1);

    comps = ast_for_comprehension(c, CHILD(n, i));
    if (!comps)
        return NULL;

    return DictComp(key, value, comps, LINENO(n), n->n_col_offset, c->c_arena);
}

static expr_ty
ast_for_dictdisplay(struct compiling *c, const node *n)
{
    int i;
    int j;
    int size;
    asdl_seq *keys, *values;

    size = (NCH(n) + 1) / 3; /* +1 in case no trailing comma */
    keys = _Py_asdl_seq_new(size, c->c_arena);
    if (!keys)
        return NULL;

    values = _Py_asdl_seq_new(size, c->c_arena);
    if (!values)
        return NULL;

    j = 0;
    for (i = 0; i < NCH(n); i++) {
        expr_ty key, value;

        if (!ast_for_dictelement(c, n, &i, &key, &value))
            return NULL;
        asdl_seq_SET(keys, j, key);
        asdl_seq_SET(values, j, value);

        j++;
    }
    keys->size = j;
    values->size = j;
    return Dict(keys, values, LINENO(n), n->n_col_offset, c->c_arena);
}

static expr_ty
ast_for_genexp(struct compiling *c, const node *n)
{
    assert(TYPE(n) == (testlist_comp) || TYPE(n) == (argument));
    return ast_for_itercomp(c, n, COMP_GENEXP);
}

static expr_ty
ast_for_listcomp(struct compiling *c, const node *n)
{
    assert(TYPE(n) == (testlist_comp));
    return ast_for_itercomp(c, n, COMP_LISTCOMP);
}

static expr_ty
ast_for_setcomp(struct compiling *c, const node *n)
{
    assert(TYPE(n) == (dictorsetmaker));
    return ast_for_itercomp(c, n, COMP_SETCOMP);
}

static expr_ty
ast_for_setdisplay(struct compiling *c, const node *n)
{
    int i;
    int size;
    asdl_seq *elts;

    assert(TYPE(n) == (dictorsetmaker));
    size = (NCH(n) + 1) / 2; /* +1 in case no trailing comma */
    elts = _Py_asdl_seq_new(size, c->c_arena);
    if (!elts)
        return NULL;
    for (i = 0; i < NCH(n); i += 2) {
        expr_ty expression;
        expression = ast_for_expr(c, CHILD(n, i));
        if (!expression)
            return NULL;
        asdl_seq_SET(elts, i / 2, expression);
    }
    return Set(elts, LINENO(n), n->n_col_offset, c->c_arena);
}

static expr_ty
ast_for_atom(struct compiling *c, const node *n)
{
    /* atom: '(' [yield_expr|testlist_comp] ')' | '[' [testlist_comp] ']'
       | '{' [dictmaker|testlist_comp] '}' | NAME | NUMBER | STRING+
       | '...' | 'None' | 'True' | 'False'
    */
    node *ch = CHILD(n, 0);

    switch (TYPE(ch)) {
    case NAME: {
        PyObject *name;
        const char *s = STR(ch);
        size_t len = strlen(s);
        if (len >= 4 && len <= 5) {
            if (!strcmp(s, "None"))
                return NameConstant(Py_None, LINENO(n), n->n_col_offset, c->c_arena);
            if (!strcmp(s, "True"))
                return NameConstant(Py_True, LINENO(n), n->n_col_offset, c->c_arena);
            if (!strcmp(s, "False"))
                return NameConstant(Py_False, LINENO(n), n->n_col_offset, c->c_arena);
        }
        name = new_identifier(s, c);
        if (!name)
            return NULL;
        /* All names start in Load context, but may later be changed. */
        return Name(name, Load, LINENO(n), n->n_col_offset, c->c_arena);
    }
    case STRING: {
        expr_ty str = parsestrplus(c, n);
        if (!str) {
            const char *errtype = NULL;
            if (PyErr_ExceptionMatches(PyExc_UnicodeError))
                errtype = "unicode error";
            else if (PyErr_ExceptionMatches(PyExc_ValueError))
                errtype = "value error";
            if (errtype) {
                char buf[128];
                PyObject *type, *value, *tback, *errstr;
                PyErr_Fetch(&type, &value, &tback);
                errstr = PyObject_Str(value);
                if (errstr) {
                    char *s = _PyUnicode_AsString(errstr);
                    PyOS_snprintf(buf, sizeof(buf), "(%s) %s", errtype, s);
                    Py_DECREF(errstr);
                } else {
                    PyErr_Clear();
                    PyOS_snprintf(buf, sizeof(buf), "(%s) unknown error", errtype);
                }
                ast_error(c, n, buf);
                Py_DECREF(type);
                Py_XDECREF(value);
                Py_XDECREF(tback);
            }
            return NULL;
        }
        return str;
    }
    case NUMBER: {
        PyObject *pynum = parsenumber(c, STR(ch));
        if (!pynum)
            return NULL;

        if (PyArena_AddPyObject(c->c_arena, pynum) < 0) {
            Py_DECREF(pynum);
            return NULL;
        }
        return Num(pynum, LINENO(n), n->n_col_offset, c->c_arena);
    }
    case ELLIPSIS: /* Ellipsis */
        return Ellipsis(LINENO(n), n->n_col_offset, c->c_arena);
    case LPAR: /* some parenthesized expressions */
        ch = CHILD(n, 1);

        if (TYPE(ch) == RPAR)
            return Tuple(NULL, Load, LINENO(n), n->n_col_offset, c->c_arena);

        if (TYPE(ch) == yield_expr)
            return ast_for_expr(c, ch);

        /* testlist_comp: test ( comp_for | (',' test)* [','] ) */
        if ((NCH(ch) > 1) && (TYPE(CHILD(ch, 1)) == comp_for))
            return ast_for_genexp(c, ch);

        return ast_for_testlist(c, ch);
    case LSQB: /* list (or list comprehension) */
        ch = CHILD(n, 1);

        if (TYPE(ch) == RSQB)
            return List(NULL, Load, LINENO(n), n->n_col_offset, c->c_arena);

        REQ(ch, testlist_comp);
        if (NCH(ch) == 1 || TYPE(CHILD(ch, 1)) == COMMA) {
            asdl_seq *elts = seq_for_testlist(c, ch);
            if (!elts)
                return NULL;

            return List(elts, Load, LINENO(n), n->n_col_offset, c->c_arena);
        }
        else
            return ast_for_listcomp(c, ch);
    case LBRACE: {
        /* dictorsetmaker: ( ((test ':' test | '**' test)
         *                    (comp_for | (',' (test ':' test | '**' test))* [','])) |
         *                   ((test | '*' test)
         *                    (comp_for | (',' (test | '*' test))* [','])) ) */
        expr_ty res;
        ch = CHILD(n, 1);
        if (TYPE(ch) == RBRACE) {
            /* It's an empty dict. */
            return Dict(NULL, NULL, LINENO(n), n->n_col_offset, c->c_arena);
        }
        else {
            int is_dict = (TYPE(CHILD(ch, 0)) == DOUBLESTAR);
            if (NCH(ch) == 1 ||
                    (NCH(ch) > 1 &&
                     TYPE(CHILD(ch, 1)) == COMMA)) {
                /* It's a set display. */
                res = ast_for_setdisplay(c, ch);
            }
            else if (NCH(ch) > 1 &&
                    TYPE(CHILD(ch, 1)) == comp_for) {
                /* It's a set comprehension. */
                res = ast_for_setcomp(c, ch);
            }
            else if (NCH(ch) > 3 - is_dict &&
                    TYPE(CHILD(ch, 3 - is_dict)) == comp_for) {
                /* It's a dictionary comprehension. */
                if (is_dict) {
                    ast_error(c, n, "dict unpacking cannot be used in "
                            "dict comprehension");
                    return NULL;
                }
                res = ast_for_dictcomp(c, ch);
            }
            else {
                /* It's a dictionary display. */
                res = ast_for_dictdisplay(c, ch);
            }
            if (res) {
                res->lineno = LINENO(n);
                res->col_offset = n->n_col_offset;
            }
            return res;
        }
    }
    default:
        PyErr_Format(PyExc_SystemError, "unhandled atom %d", TYPE(ch));
        return NULL;
    }
}

static slice_ty
ast_for_slice(struct compiling *c, const node *n)
{
    node *ch;
    expr_ty lower = NULL, upper = NULL, step = NULL;

    REQ(n, subscript);

    /*
       subscript: test | [test] ':' [test] [sliceop]
       sliceop: ':' [test]
    */
    ch = CHILD(n, 0);
    if (NCH(n) == 1 && TYPE(ch) == test) {
        /* 'step' variable hold no significance in terms of being used over
           other vars */
        step = ast_for_expr(c, ch);
        if (!step)
            return NULL;

        return Index(step, c->c_arena);
    }

    if (TYPE(ch) == test) {
        lower = ast_for_expr(c, ch);
        if (!lower)
            return NULL;
    }

    /* If there's an upper bound it's in the second or third position. */
    if (TYPE(ch) == COLON) {
        if (NCH(n) > 1) {
            node *n2 = CHILD(n, 1);

            if (TYPE(n2) == test) {
                upper = ast_for_expr(c, n2);
                if (!upper)
                    return NULL;
            }
        }
    } else if (NCH(n) > 2) {
        node *n2 = CHILD(n, 2);

        if (TYPE(n2) == test) {
            upper = ast_for_expr(c, n2);
            if (!upper)
                return NULL;
        }
    }

    ch = CHILD(n, NCH(n) - 1);
    if (TYPE(ch) == sliceop) {
        if (NCH(ch) != 1) {
            ch = CHILD(ch, 1);
            if (TYPE(ch) == test) {
                step = ast_for_expr(c, ch);
                if (!step)
                    return NULL;
            }
        }
    }

    return Slice(lower, upper, step, c->c_arena);
}

static expr_ty
ast_for_binop(struct compiling *c, const node *n)
{
    /* Must account for a sequence of expressions.
       How should A op B op C by represented?
       BinOp(BinOp(A, op, B), op, C).
    */

    int i, nops;
    expr_ty expr1, expr2, result;
    operator_ty newoperator;

    expr1 = ast_for_expr(c, CHILD(n, 0));
    if (!expr1)
        return NULL;

    expr2 = ast_for_expr(c, CHILD(n, 2));
    if (!expr2)
        return NULL;

    newoperator = get_operator(CHILD(n, 1));
    if (!newoperator)
        return NULL;

    result = BinOp(expr1, newoperator, expr2, LINENO(n), n->n_col_offset,
                   c->c_arena);
    if (!result)
        return NULL;

    nops = (NCH(n) - 1) / 2;
    for (i = 1; i < nops; i++) {
        expr_ty tmp_result, tmp;
        const node* next_oper = CHILD(n, i * 2 + 1);

        newoperator = get_operator(next_oper);
        if (!newoperator)
            return NULL;

        tmp = ast_for_expr(c, CHILD(n, i * 2 + 2));
        if (!tmp)
            return NULL;

        tmp_result = BinOp(result, newoperator, tmp,
                           LINENO(next_oper), next_oper->n_col_offset,
                           c->c_arena);
        if (!tmp_result)
            return NULL;
        result = tmp_result;
    }
    return result;
}

static expr_ty
ast_for_trailer(struct compiling *c, const node *n, expr_ty left_expr)
{
    /* trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME
       subscriptlist: subscript (',' subscript)* [',']
       subscript: '.' '.' '.' | test | [test] ':' [test] [sliceop]
     */
    REQ(n, trailer);
    if (TYPE(CHILD(n, 0)) == LPAR) {
        if (NCH(n) == 2)
            return Call(left_expr, NULL, NULL, LINENO(n),
                        n->n_col_offset, c->c_arena);
        else
            return ast_for_call(c, CHILD(n, 1), left_expr);
    }
    else if (TYPE(CHILD(n, 0)) == DOT) {
        PyObject *attr_id = NEW_IDENTIFIER(CHILD(n, 1));
        if (!attr_id)
            return NULL;
        return Attribute(left_expr, attr_id, Load,
                         LINENO(n), n->n_col_offset, c->c_arena);
    }
    else {
        REQ(CHILD(n, 0), LSQB);
        REQ(CHILD(n, 2), RSQB);
        n = CHILD(n, 1);
        if (NCH(n) == 1) {
            slice_ty slc = ast_for_slice(c, CHILD(n, 0));
            if (!slc)
                return NULL;
            return Subscript(left_expr, slc, Load, LINENO(n), n->n_col_offset,
                             c->c_arena);
        }
        else {
            /* The grammar is ambiguous here. The ambiguity is resolved
               by treating the sequence as a tuple literal if there are
               no slice features.
            */
            int j;
            slice_ty slc;
            expr_ty e;
            int simple = 1;
            asdl_seq *slices, *elts;
            slices = _Py_asdl_seq_new((NCH(n) + 1) / 2, c->c_arena);
            if (!slices)
                return NULL;
            for (j = 0; j < NCH(n); j += 2) {
                slc = ast_for_slice(c, CHILD(n, j));
                if (!slc)
                    return NULL;
                if (slc->kind != Index_kind)
                    simple = 0;
                asdl_seq_SET(slices, j / 2, slc);
            }
            if (!simple) {
                return Subscript(left_expr, ExtSlice(slices, c->c_arena),
                                 Load, LINENO(n), n->n_col_offset, c->c_arena);
            }
            /* extract Index values and put them in a Tuple */
            elts = _Py_asdl_seq_new(asdl_seq_LEN(slices), c->c_arena);
            if (!elts)
                return NULL;
            for (j = 0; j < asdl_seq_LEN(slices); ++j) {
                slc = (slice_ty)asdl_seq_GET(slices, j);
                assert(slc->kind == Index_kind  && slc->v.Index.value);
                asdl_seq_SET(elts, j, slc->v.Index.value);
            }
            e = Tuple(elts, Load, LINENO(n), n->n_col_offset, c->c_arena);
            if (!e)
                return NULL;
            return Subscript(left_expr, Index(e, c->c_arena),
                             Load, LINENO(n), n->n_col_offset, c->c_arena);
        }
    }
}

static expr_ty
ast_for_factor(struct compiling *c, const node *n)
{
    expr_ty expression;

    expression = ast_for_expr(c, CHILD(n, 1));
    if (!expression)
        return NULL;

    switch (TYPE(CHILD(n, 0))) {
        case PLUS:
            return UnaryOp(UAdd, expression, LINENO(n), n->n_col_offset,
                           c->c_arena);
        case MINUS:
            return UnaryOp(USub, expression, LINENO(n), n->n_col_offset,
                           c->c_arena);
        case TILDE:
            return UnaryOp(Invert, expression, LINENO(n),
                           n->n_col_offset, c->c_arena);
    }
    PyErr_Format(PyExc_SystemError, "unhandled factor: %d",
                 TYPE(CHILD(n, 0)));
    return NULL;
}

static expr_ty
ast_for_atom_expr(struct compiling *c, const node *n)
{
    int i, nch, start = 0;
    expr_ty e, tmp;

    REQ(n, atom_expr);
    nch = NCH(n);

    if (TYPE(CHILD(n, 0)) == AWAIT) {
        start = 1;
        assert(nch > 1);
    }

    e = ast_for_atom(c, CHILD(n, start));
    if (!e)
        return NULL;
    if (nch == 1)
        return e;
    if (start && nch == 2) {
        return Await(e, LINENO(n), n->n_col_offset, c->c_arena);
    }

    for (i = start + 1; i < nch; i++) {
        node *ch = CHILD(n, i);
        if (TYPE(ch) != trailer)
            break;
        tmp = ast_for_trailer(c, ch, e);
        if (!tmp)
            return NULL;
        tmp->lineno = e->lineno;
        tmp->col_offset = e->col_offset;
        e = tmp;
    }

    if (start) {
        /* there was an AWAIT */
        return Await(e, LINENO(n), n->n_col_offset, c->c_arena);
    }
    else {
        return e;
    }
}

static expr_ty
ast_for_power(struct compiling *c, const node *n)
{
    /* power: atom trailer* ('**' factor)*
     */
    expr_ty e;
    REQ(n, power);
    e = ast_for_atom_expr(c, CHILD(n, 0));
    if (!e)
        return NULL;
    if (NCH(n) == 1)
        return e;
    if (TYPE(CHILD(n, NCH(n) - 1)) == factor) {
        expr_ty f = ast_for_expr(c, CHILD(n, NCH(n) - 1));
        if (!f)
            return NULL;
        e = BinOp(e, Pow, f, LINENO(n), n->n_col_offset, c->c_arena);
    }
    return e;
}

static expr_ty
ast_for_starred(struct compiling *c, const node *n)
{
    expr_ty tmp;
    REQ(n, star_expr);

    tmp = ast_for_expr(c, CHILD(n, 1));
    if (!tmp)
        return NULL;

    /* The Load context is changed later. */
    return Starred(tmp, Load, LINENO(n), n->n_col_offset, c->c_arena);
}


/* Do not name a variable 'expr'!  Will cause a compile error.
*/

static expr_ty
ast_for_expr(struct compiling *c, const node *n)
{
    /* handle the full range of simple expressions
       test: or_test ['if' or_test 'else' test] | lambdef
       test_nocond: or_test | lambdef_nocond
       or_test: and_test ('or' and_test)*
       and_test: not_test ('and' not_test)*
       not_test: 'not' not_test | comparison
       comparison: expr (comp_op expr)*
       expr: xor_expr ('|' xor_expr)*
       xor_expr: and_expr ('^' and_expr)*
       and_expr: shift_expr ('&' shift_expr)*
       shift_expr: arith_expr (('<<'|'>>') arith_expr)*
       arith_expr: term (('+'|'-') term)*
       term: factor (('*'|'@'|'/'|'%'|'//') factor)*
       factor: ('+'|'-'|'~') factor | power
       power: atom_expr ['**' factor]
       atom_expr: [AWAIT] atom trailer*
       yield_expr: 'yield' [yield_arg]
    */

    asdl_seq *seq;
    int i;

 loop:
    switch (TYPE(n)) {
        case test:
        case test_nocond:
            if (TYPE(CHILD(n, 0)) == lambdef ||
                TYPE(CHILD(n, 0)) == lambdef_nocond)
                return ast_for_lambdef(c, CHILD(n, 0));
            else if (NCH(n) > 1)
                return ast_for_ifexpr(c, n);
            /* Fallthrough */
        case or_test:
        case and_test:
            if (NCH(n) == 1) {
                n = CHILD(n, 0);
                goto loop;
            }
            seq = _Py_asdl_seq_new((NCH(n) + 1) / 2, c->c_arena);
            if (!seq)
                return NULL;
            for (i = 0; i < NCH(n); i += 2) {
                expr_ty e = ast_for_expr(c, CHILD(n, i));
                if (!e)
                    return NULL;
                asdl_seq_SET(seq, i / 2, e);
            }
            if (!strcmp(STR(CHILD(n, 1)), "and"))
                return BoolOp(And, seq, LINENO(n), n->n_col_offset,
                              c->c_arena);
            assert(!strcmp(STR(CHILD(n, 1)), "or"));
            return BoolOp(Or, seq, LINENO(n), n->n_col_offset, c->c_arena);
        case not_test:
            if (NCH(n) == 1) {
                n = CHILD(n, 0);
                goto loop;
            }
            else {
                expr_ty expression = ast_for_expr(c, CHILD(n, 1));
                if (!expression)
                    return NULL;

                return UnaryOp(Not, expression, LINENO(n), n->n_col_offset,
                               c->c_arena);
            }
        case comparison:
            if (NCH(n) == 1) {
                n = CHILD(n, 0);
                goto loop;
            }
            else {
                expr_ty expression;
                asdl_int_seq *ops;
                asdl_seq *cmps;
                ops = _Py_asdl_int_seq_new(NCH(n) / 2, c->c_arena);
                if (!ops)
                    return NULL;
                cmps = _Py_asdl_seq_new(NCH(n) / 2, c->c_arena);
                if (!cmps) {
                    return NULL;
                }
                for (i = 1; i < NCH(n); i += 2) {
                    cmpop_ty newoperator;

                    newoperator = ast_for_comp_op(c, CHILD(n, i));
                    if (!newoperator) {
                        return NULL;
                    }

                    expression = ast_for_expr(c, CHILD(n, i + 1));
                    if (!expression) {
                        return NULL;
                    }

                    asdl_seq_SET(ops, i / 2, newoperator);
                    asdl_seq_SET(cmps, i / 2, expression);
                }
                expression = ast_for_expr(c, CHILD(n, 0));
                if (!expression) {
                    return NULL;
                }

                return Compare(expression, ops, cmps, LINENO(n),
                               n->n_col_offset, c->c_arena);
            }
            break;

        case star_expr:
            return ast_for_starred(c, n);
        /* The next five cases all handle BinOps.  The main body of code
           is the same in each case, but the switch turned inside out to
           reuse the code for each type of operator.
         */
        case expr:
        case xor_expr:
        case and_expr:
        case shift_expr:
        case arith_expr:
        case term:
            if (NCH(n) == 1) {
                n = CHILD(n, 0);
                goto loop;
            }
            return ast_for_binop(c, n);
        case yield_expr: {
            node *an = NULL;
            node *en = NULL;
            int is_from = 0;
            expr_ty exp = NULL;
            if (NCH(n) > 1)
                an = CHILD(n, 1); /* yield_arg */
            if (an) {
                en = CHILD(an, NCH(an) - 1);
                if (NCH(an) == 2) {
                    is_from = 1;
                    exp = ast_for_expr(c, en);
                }
                else
                    exp = ast_for_testlist(c, en);
                if (!exp)
                    return NULL;
            }
            if (is_from)
                return YieldFrom(exp, LINENO(n), n->n_col_offset, c->c_arena);
            return Yield(exp, LINENO(n), n->n_col_offset, c->c_arena);
        }
        case factor:
            if (NCH(n) == 1) {
                n = CHILD(n, 0);
                goto loop;
            }
            return ast_for_factor(c, n);
        case power:
            return ast_for_power(c, n);
        default:
            PyErr_Format(PyExc_SystemError, "unhandled expr: %d", TYPE(n));
            return NULL;
    }
    /* should never get here unless if error is set */
    return NULL;
}

static expr_ty
ast_for_call(struct compiling *c, const node *n, expr_ty func)
{
    /*
      arglist: argument (',' argument)*  [',']
      argument: ( test [comp_for] | '*' test | test '=' test | '**' test )
    */

    int i, nargs, nkeywords, ngens;
    int ndoublestars;
    asdl_seq *args;
    asdl_seq *keywords;

    REQ(n, arglist);

    nargs = 0;
    nkeywords = 0;
    ngens = 0;
    for (i = 0; i < NCH(n); i++) {
        node *ch = CHILD(n, i);
        if (TYPE(ch) == argument) {
            if (NCH(ch) == 1)
                nargs++;
            else if (TYPE(CHILD(ch, 1)) == comp_for)
                ngens++;
            else if (TYPE(CHILD(ch, 0)) == STAR)
                nargs++;
            else
                /* TYPE(CHILD(ch, 0)) == DOUBLESTAR or keyword argument */
                nkeywords++;
        }
    }
    if (ngens > 1 || (ngens && (nargs || nkeywords))) {
        ast_error(c, n, "Generator expression must be parenthesized "
                  "if not sole argument");
        return NULL;
    }

    if (nargs + nkeywords + ngens > 255) {
        ast_error(c, n, "more than 255 arguments");
        return NULL;
    }

    args = _Py_asdl_seq_new(nargs + ngens, c->c_arena);
    if (!args)
        return NULL;
    keywords = _Py_asdl_seq_new(nkeywords, c->c_arena);
    if (!keywords)
        return NULL;

    nargs = 0;  /* positional arguments + iterable argument unpackings */
    nkeywords = 0;  /* keyword arguments + keyword argument unpackings */
    ndoublestars = 0;  /* just keyword argument unpackings */
    for (i = 0; i < NCH(n); i++) {
        node *ch = CHILD(n, i);
        if (TYPE(ch) == argument) {
            expr_ty e;
            node *chch = CHILD(ch, 0);
            if (NCH(ch) == 1) {
                /* a positional argument */
                if (nkeywords) {
                    if (ndoublestars) {
                        ast_error(c, chch,
                                "positional argument follows "
                                "keyword argument unpacking");
                    }
                    else {
                        ast_error(c, chch,
                                "positional argument follows "
                                "keyword argument");
                    }
                    return NULL;
                }
                e = ast_for_expr(c, chch);
                if (!e)
                    return NULL;
                asdl_seq_SET(args, nargs++, e);
            }
            else if (TYPE(chch) == STAR) {
                /* an iterable argument unpacking */
                expr_ty starred;
                if (ndoublestars) {
                    ast_error(c, chch,
                            "iterable argument unpacking follows "
                            "keyword argument unpacking");
                    return NULL;
                }
                e = ast_for_expr(c, CHILD(ch, 1));
                if (!e)
                    return NULL;
                starred = Starred(e, Load, LINENO(chch),
                        chch->n_col_offset,
                        c->c_arena);
                if (!starred)
                    return NULL;
                asdl_seq_SET(args, nargs++, starred);

            }
            else if (TYPE(chch) == DOUBLESTAR) {
                /* a keyword argument unpacking */
                keyword_ty kw;
                i++;
                e = ast_for_expr(c, CHILD(ch, 1));
                if (!e)
                    return NULL;
                kw = keyword(NULL, e, c->c_arena);
                asdl_seq_SET(keywords, nkeywords++, kw);
                ndoublestars++;
            }
            else if (TYPE(CHILD(ch, 1)) == comp_for) {
                /* the lone generator expression */
                e = ast_for_genexp(c, ch);
                if (!e)
                    return NULL;
                asdl_seq_SET(args, nargs++, e);
            }
            else {
                /* a keyword argument */
                keyword_ty kw;
                identifier key, tmp;
                int k;

                /* chch is test, but must be an identifier? */
                e = ast_for_expr(c, chch);
                if (!e)
                    return NULL;
                /* f(lambda x: x[0] = 3) ends up getting parsed with
                 * LHS test = lambda x: x[0], and RHS test = 3.
                 * SF bug 132313 points out that complaining about a keyword
                 * then is very confusing.
                 */
                if (e->kind == Lambda_kind) {
                    ast_error(c, chch,
                            "lambda cannot contain assignment");
                    return NULL;
                }
                else if (e->kind != Name_kind) {
                    ast_error(c, chch,
                            "keyword can't be an expression");
                    return NULL;
                }
                else if (forbidden_name(c, e->v.Name.id, ch, 1)) {
                    return NULL;
                }
                key = e->v.Name.id;
                for (k = 0; k < nkeywords; k++) {
                    tmp = ((keyword_ty)asdl_seq_GET(keywords, k))->arg;
                    if (tmp && !PyUnicode_Compare(tmp, key)) {
                        ast_error(c, chch,
                                "keyword argument repeated");
                        return NULL;
                    }
                }
                e = ast_for_expr(c, CHILD(ch, 2));
                if (!e)
                    return NULL;
                kw = keyword(key, e, c->c_arena);
                if (!kw)
                    return NULL;
                asdl_seq_SET(keywords, nkeywords++, kw);
            }
        }
    }

    return Call(func, args, keywords, func->lineno, func->col_offset, c->c_arena);
}

static expr_ty
ast_for_testlist(struct compiling *c, const node* n)
{
    /* testlist_comp: test (comp_for | (',' test)* [',']) */
    /* testlist: test (',' test)* [','] */
    assert(NCH(n) > 0);
    if (TYPE(n) == testlist_comp) {
        if (NCH(n) > 1)
            assert(TYPE(CHILD(n, 1)) != comp_for);
    }
    else {
        assert(TYPE(n) == testlist ||
               TYPE(n) == testlist_star_expr);
    }
    if (NCH(n) == 1)
        return ast_for_expr(c, CHILD(n, 0));
    else {
        asdl_seq *tmp = seq_for_testlist(c, n);
        if (!tmp)
            return NULL;
        return Tuple(tmp, Load, LINENO(n), n->n_col_offset, c->c_arena);
    }
}

static stmt_ty
ast_for_expr_stmt(struct compiling *c, const node *n)
{
    REQ(n, expr_stmt);
    /* expr_stmt: testlist_star_expr (augassign (yield_expr|testlist)
                | ('=' (yield_expr|testlist))*)
       testlist_star_expr: (test|star_expr) (',' test|star_expr)* [',']
       augassign: '+=' | '-=' | '*=' | '@=' | '/=' | '%=' | '&=' | '|=' | '^='
                | '<<=' | '>>=' | '**=' | '//='
       test: ... here starts the operator precendence dance
     */

    if (NCH(n) == 1) {
        expr_ty e = ast_for_testlist(c, CHILD(n, 0));
        if (!e)
            return NULL;

        return Expr(e, LINENO(n), n->n_col_offset, c->c_arena);
    }
    else if (TYPE(CHILD(n, 1)) == augassign) {
        expr_ty expr1, expr2;
        operator_ty newoperator;
        node *ch = CHILD(n, 0);

        expr1 = ast_for_testlist(c, ch);
        if (!expr1)
            return NULL;
        if(!set_context(c, expr1, Store, ch))
            return NULL;
        /* set_context checks that most expressions are not the left side.
          Augmented assignments can only have a name, a subscript, or an
          attribute on the left, though, so we have to explicitly check for
          those. */
        switch (expr1->kind) {
            case Name_kind:
            case Attribute_kind:
            case Subscript_kind:
                break;
            default:
                ast_error(c, ch, "illegal expression for augmented assignment");
                return NULL;
        }

        ch = CHILD(n, 2);
        if (TYPE(ch) == testlist)
            expr2 = ast_for_testlist(c, ch);
        else
            expr2 = ast_for_expr(c, ch);
        if (!expr2)
            return NULL;

        newoperator = ast_for_augassign(c, CHILD(n, 1));
        if (!newoperator)
            return NULL;

        return AugAssign(expr1, newoperator, expr2, LINENO(n), n->n_col_offset, c->c_arena);
    }
    else {
        int i;
        asdl_seq *targets;
        node *value;
        expr_ty expression;

        /* a normal assignment */
        REQ(CHILD(n, 1), EQUAL);
        targets = _Py_asdl_seq_new(NCH(n) / 2, c->c_arena);
        if (!targets)
            return NULL;
        for (i = 0; i < NCH(n) - 2; i += 2) {
            expr_ty e;
            node *ch = CHILD(n, i);
            if (TYPE(ch) == yield_expr) {
                ast_error(c, ch, "assignment to yield expression not possible");
                return NULL;
            }
            e = ast_for_testlist(c, ch);
            if (!e)
              return NULL;

            /* set context to assign */
            if (!set_context(c, e, Store, CHILD(n, i)))
              return NULL;

            asdl_seq_SET(targets, i / 2, e);
        }
        value = CHILD(n, NCH(n) - 1);
        if (TYPE(value) == testlist_star_expr)
            expression = ast_for_testlist(c, value);
        else
            expression = ast_for_expr(c, value);
        if (!expression)
            return NULL;
        return Assign(targets, expression, LINENO(n), n->n_col_offset, c->c_arena);
    }
}


static asdl_seq *
ast_for_exprlist(struct compiling *c, const node *n, expr_context_ty context)
{
    asdl_seq *seq;
    int i;
    expr_ty e;

    REQ(n, exprlist);

    seq = _Py_asdl_seq_new((NCH(n) + 1) / 2, c->c_arena);
    if (!seq)
        return NULL;
    for (i = 0; i < NCH(n); i += 2) {
        e = ast_for_expr(c, CHILD(n, i));
        if (!e)
            return NULL;
        asdl_seq_SET(seq, i / 2, e);
        if (context && !set_context(c, e, context, CHILD(n, i)))
            return NULL;
    }
    return seq;
}

static stmt_ty
ast_for_del_stmt(struct compiling *c, const node *n)
{
    asdl_seq *expr_list;

    /* del_stmt: 'del' exprlist */
    REQ(n, del_stmt);

    expr_list = ast_for_exprlist(c, CHILD(n, 1), Del);
    if (!expr_list)
        return NULL;
    return Delete(expr_list, LINENO(n), n->n_col_offset, c->c_arena);
}

static stmt_ty
ast_for_flow_stmt(struct compiling *c, const node *n)
{
    /*
      flow_stmt: break_stmt | continue_stmt | return_stmt | raise_stmt
                 | yield_stmt
      break_stmt: 'break'
      continue_stmt: 'continue'
      return_stmt: 'return' [testlist]
      yield_stmt: yield_expr
      yield_expr: 'yield' testlist | 'yield' 'from' test
      raise_stmt: 'raise' [test [',' test [',' test]]]
    */
    node *ch;

    REQ(n, flow_stmt);
    ch = CHILD(n, 0);
    switch (TYPE(ch)) {
        case break_stmt:
            return Break(LINENO(n), n->n_col_offset, c->c_arena);
        case continue_stmt:
            return Continue(LINENO(n), n->n_col_offset, c->c_arena);
        case yield_stmt: { /* will reduce to yield_expr */
            expr_ty exp = ast_for_expr(c, CHILD(ch, 0));
            if (!exp)
                return NULL;
            return Expr(exp, LINENO(n), n->n_col_offset, c->c_arena);
        }
        case return_stmt:
            if (NCH(ch) == 1)
                return Return(NULL, LINENO(n), n->n_col_offset, c->c_arena);
            else {
                expr_ty expression = ast_for_testlist(c, CHILD(ch, 1));
                if (!expression)
                    return NULL;
                return Return(expression, LINENO(n), n->n_col_offset, c->c_arena);
            }
        case raise_stmt:
            if (NCH(ch) == 1)
                return Raise(NULL, NULL, LINENO(n), n->n_col_offset, c->c_arena);
            else if (NCH(ch) >= 2) {
                expr_ty cause = NULL;
                expr_ty expression = ast_for_expr(c, CHILD(ch, 1));
                if (!expression)
                    return NULL;
                if (NCH(ch) == 4) {
                    cause = ast_for_expr(c, CHILD(ch, 3));
                    if (!cause)
                        return NULL;
                }
                return Raise(expression, cause, LINENO(n), n->n_col_offset, c->c_arena);
            }
        default:
            PyErr_Format(PyExc_SystemError,
                         "unexpected flow_stmt: %d", TYPE(ch));
            return NULL;
    }

    PyErr_SetString(PyExc_SystemError, "unhandled flow statement");
    return NULL;
}

static alias_ty
alias_for_import_name(struct compiling *c, const node *n, int store)
{
    /*
      import_as_name: NAME ['as' NAME]
      dotted_as_name: dotted_name ['as' NAME]
      dotted_name: NAME ('.' NAME)*
    */
    identifier str, name;

 loop:
    switch (TYPE(n)) {
        case import_as_name: {
            node *name_node = CHILD(n, 0);
            str = NULL;
            name = NEW_IDENTIFIER(name_node);
            if (!name)
                return NULL;
            if (NCH(n) == 3) {
                node *str_node = CHILD(n, 2);
                str = NEW_IDENTIFIER(str_node);
                if (!str)
                    return NULL;
                if (store && forbidden_name(c, str, str_node, 0))
                    return NULL;
            }
            else {
                if (forbidden_name(c, name, name_node, 0))
                    return NULL;
            }
            return alias(name, str, c->c_arena);
        }
        case dotted_as_name:
            if (NCH(n) == 1) {
                n = CHILD(n, 0);
                goto loop;
            }
            else {
                node *asname_node = CHILD(n, 2);
                alias_ty a = alias_for_import_name(c, CHILD(n, 0), 0);
                if (!a)
                    return NULL;
                assert(!a->asname);
                a->asname = NEW_IDENTIFIER(asname_node);
                if (!a->asname)
                    return NULL;
                if (forbidden_name(c, a->asname, asname_node, 0))
                    return NULL;
                return a;
            }
            break;
        case dotted_name:
            if (NCH(n) == 1) {
                node *name_node = CHILD(n, 0);
                name = NEW_IDENTIFIER(name_node);
                if (!name)
                    return NULL;
                if (store && forbidden_name(c, name, name_node, 0))
                    return NULL;
                return alias(name, NULL, c->c_arena);
            }
            else {
                /* Create a string of the form "a.b.c" */
                int i;
                size_t len;
                char *s;
                PyObject *uni;

                len = 0;
                for (i = 0; i < NCH(n); i += 2)
                    /* length of string plus one for the dot */
                    len += strlen(STR(CHILD(n, i))) + 1;
                len--; /* the last name doesn't have a dot */
                str = PyBytes_FromStringAndSize(NULL, len);
                if (!str)
                    return NULL;
                s = PyBytes_AS_STRING(str);
                if (!s)
                    return NULL;
                for (i = 0; i < NCH(n); i += 2) {
                    char *sch = STR(CHILD(n, i));
                    strcpy(s, STR(CHILD(n, i)));
                    s += strlen(sch);
                    *s++ = '.';
                }
                --s;
                *s = '\0';
                uni = PyUnicode_DecodeUTF8(PyBytes_AS_STRING(str),
                                           PyBytes_GET_SIZE(str),
                                           NULL);
                Py_DECREF(str);
                if (!uni)
                    return NULL;
                str = uni;
                PyUnicode_InternInPlace(&str);
                if (PyArena_AddPyObject(c->c_arena, str) < 0) {
                    Py_DECREF(str);
                    return NULL;
                }
                return alias(str, NULL, c->c_arena);
            }
            break;
        case STAR:
            str = PyUnicode_InternFromString("*");
            if (PyArena_AddPyObject(c->c_arena, str) < 0) {
                Py_DECREF(str);
                return NULL;
            }
            return alias(str, NULL, c->c_arena);
        default:
            PyErr_Format(PyExc_SystemError,
                         "unexpected import name: %d", TYPE(n));
            return NULL;
    }

    PyErr_SetString(PyExc_SystemError, "unhandled import name condition");
    return NULL;
}

static stmt_ty
ast_for_import_stmt(struct compiling *c, const node *n)
{
    /*
      import_stmt: import_name | import_from
      import_name: 'import' dotted_as_names
      import_from: 'from' (('.' | '...')* dotted_name | ('.' | '...')+)
                   'import' ('*' | '(' import_as_names ')' | import_as_names)
    */
    int lineno;
    int col_offset;
    int i;
    asdl_seq *aliases;

    REQ(n, import_stmt);
    lineno = LINENO(n);
    col_offset = n->n_col_offset;
    n = CHILD(n, 0);
    if (TYPE(n) == import_name) {
        n = CHILD(n, 1);
        REQ(n, dotted_as_names);
        aliases = _Py_asdl_seq_new((NCH(n) + 1) / 2, c->c_arena);
        if (!aliases)
                return NULL;
        for (i = 0; i < NCH(n); i += 2) {
            alias_ty import_alias = alias_for_import_name(c, CHILD(n, i), 1);
            if (!import_alias)
                return NULL;
            asdl_seq_SET(aliases, i / 2, import_alias);
        }
        return Import(aliases, lineno, col_offset, c->c_arena);
    }
    else if (TYPE(n) == import_from) {
        int n_children;
        int idx, ndots = 0;
        alias_ty mod = NULL;
        identifier modname = NULL;

       /* Count the number of dots (for relative imports) and check for the
          optional module name */
        for (idx = 1; idx < NCH(n); idx++) {
            if (TYPE(CHILD(n, idx)) == dotted_name) {
                mod = alias_for_import_name(c, CHILD(n, idx), 0);
                if (!mod)
                    return NULL;
                idx++;
                break;
            } else if (TYPE(CHILD(n, idx)) == ELLIPSIS) {
                /* three consecutive dots are tokenized as one ELLIPSIS */
                ndots += 3;
                continue;
            } else if (TYPE(CHILD(n, idx)) != DOT) {
                break;
            }
            ndots++;
        }
        idx++; /* skip over the 'import' keyword */
        switch (TYPE(CHILD(n, idx))) {
        case STAR:
            /* from ... import * */
            n = CHILD(n, idx);
            n_children = 1;
            break;
        case LPAR:
            /* from ... import (x, y, z) */
            n = CHILD(n, idx + 1);
            n_children = NCH(n);
            break;
        case import_as_names:
            /* from ... import x, y, z */
            n = CHILD(n, idx);
            n_children = NCH(n);
            if (n_children % 2 == 0) {
                ast_error(c, n, "trailing comma not allowed without"
                             " surrounding parentheses");
                return NULL;
            }
            break;
        default:
            ast_error(c, n, "Unexpected node-type in from-import");
            return NULL;
        }

        aliases = _Py_asdl_seq_new((n_children + 1) / 2, c->c_arena);
        if (!aliases)
            return NULL;

        /* handle "from ... import *" special b/c there's no children */
        if (TYPE(n) == STAR) {
            alias_ty import_alias = alias_for_import_name(c, n, 1);
            if (!import_alias)
                return NULL;
                asdl_seq_SET(aliases, 0, import_alias);
        }
        else {
            for (i = 0; i < NCH(n); i += 2) {
                alias_ty import_alias = alias_for_import_name(c, CHILD(n, i), 1);
                if (!import_alias)
                    return NULL;
                    asdl_seq_SET(aliases, i / 2, import_alias);
            }
        }
        if (mod != NULL)
            modname = mod->name;
        return ImportFrom(modname, aliases, ndots, lineno, col_offset,
                          c->c_arena);
    }
    PyErr_Format(PyExc_SystemError,
                 "unknown import statement: starts with command '%s'",
                 STR(CHILD(n, 0)));
    return NULL;
}

static stmt_ty
ast_for_global_stmt(struct compiling *c, const node *n)
{
    /* global_stmt: 'global' NAME (',' NAME)* */
    identifier name;
    asdl_seq *s;
    int i;

    REQ(n, global_stmt);
    s = _Py_asdl_seq_new(NCH(n) / 2, c->c_arena);
    if (!s)
        return NULL;
    for (i = 1; i < NCH(n); i += 2) {
        name = NEW_IDENTIFIER(CHILD(n, i));
        if (!name)
            return NULL;
        asdl_seq_SET(s, i / 2, name);
    }
    return Global(s, LINENO(n), n->n_col_offset, c->c_arena);
}

static stmt_ty
ast_for_nonlocal_stmt(struct compiling *c, const node *n)
{
    /* nonlocal_stmt: 'nonlocal' NAME (',' NAME)* */
    identifier name;
    asdl_seq *s;
    int i;

    REQ(n, nonlocal_stmt);
    s = _Py_asdl_seq_new(NCH(n) / 2, c->c_arena);
    if (!s)
        return NULL;
    for (i = 1; i < NCH(n); i += 2) {
        name = NEW_IDENTIFIER(CHILD(n, i));
        if (!name)
            return NULL;
        asdl_seq_SET(s, i / 2, name);
    }
    return Nonlocal(s, LINENO(n), n->n_col_offset, c->c_arena);
}

static stmt_ty
ast_for_assert_stmt(struct compiling *c, const node *n)
{
    /* assert_stmt: 'assert' test [',' test] */
    REQ(n, assert_stmt);
    if (NCH(n) == 2) {
        expr_ty expression = ast_for_expr(c, CHILD(n, 1));
        if (!expression)
            return NULL;
        return Assert(expression, NULL, LINENO(n), n->n_col_offset, c->c_arena);
    }
    else if (NCH(n) == 4) {
        expr_ty expr1, expr2;

        expr1 = ast_for_expr(c, CHILD(n, 1));
        if (!expr1)
            return NULL;
        expr2 = ast_for_expr(c, CHILD(n, 3));
        if (!expr2)
            return NULL;

        return Assert(expr1, expr2, LINENO(n), n->n_col_offset, c->c_arena);
    }
    PyErr_Format(PyExc_SystemError,
                 "improper number of parts to 'assert' statement: %d",
                 NCH(n));
    return NULL;
}

static asdl_seq *
ast_for_suite(struct compiling *c, const node *n)
{
    /* suite: simple_stmt | NEWLINE INDENT stmt+ DEDENT */
    asdl_seq *seq;
    stmt_ty s;
    int i, total, num, end, pos = 0;
    node *ch;

    REQ(n, suite);

    total = num_stmts(n);
    seq = _Py_asdl_seq_new(total, c->c_arena);
    if (!seq)
        return NULL;
    if (TYPE(CHILD(n, 0)) == simple_stmt) {
        n = CHILD(n, 0);
        /* simple_stmt always ends with a NEWLINE,
           and may have a trailing SEMI
        */
        end = NCH(n) - 1;
        if (TYPE(CHILD(n, end - 1)) == SEMI)
            end--;
        /* loop by 2 to skip semi-colons */
        for (i = 0; i < end; i += 2) {
            ch = CHILD(n, i);
            s = ast_for_stmt(c, ch);
            if (!s)
                return NULL;
            asdl_seq_SET(seq, pos++, s);
        }
    }
    else {
        for (i = 2; i < (NCH(n) - 1); i++) {
            ch = CHILD(n, i);
            REQ(ch, stmt);
            num = num_stmts(ch);
            if (num == 1) {
                /* small_stmt or compound_stmt with only one child */
                s = ast_for_stmt(c, ch);
                if (!s)
                    return NULL;
                asdl_seq_SET(seq, pos++, s);
            }
            else {
                int j;
                ch = CHILD(ch, 0);
                REQ(ch, simple_stmt);
                for (j = 0; j < NCH(ch); j += 2) {
                    /* statement terminates with a semi-colon ';' */
                    if (NCH(CHILD(ch, j)) == 0) {
                        assert((j + 1) == NCH(ch));
                        break;
                    }
                    s = ast_for_stmt(c, CHILD(ch, j));
                    if (!s)
                        return NULL;
                    asdl_seq_SET(seq, pos++, s);
                }
            }
        }
    }
    assert(pos == seq->size);
    return seq;
}

static stmt_ty
ast_for_if_stmt(struct compiling *c, const node *n)
{
    /* if_stmt: 'if' test ':' suite ('elif' test ':' suite)*
       ['else' ':' suite]
    */
    char *s;

    REQ(n, if_stmt);

    if (NCH(n) == 4) {
        expr_ty expression;
        asdl_seq *suite_seq;

        expression = ast_for_expr(c, CHILD(n, 1));
        if (!expression)
            return NULL;
        suite_seq = ast_for_suite(c, CHILD(n, 3));
        if (!suite_seq)
            return NULL;

        return If(expression, suite_seq, NULL, LINENO(n), n->n_col_offset,
                  c->c_arena);
    }

    s = STR(CHILD(n, 4));
    /* s[2], the third character in the string, will be
       's' for el_s_e, or
       'i' for el_i_f
    */
    if (s[2] == 's') {
        expr_ty expression;
        asdl_seq *seq1, *seq2;

        expression = ast_for_expr(c, CHILD(n, 1));
        if (!expression)
            return NULL;
        seq1 = ast_for_suite(c, CHILD(n, 3));
        if (!seq1)
            return NULL;
        seq2 = ast_for_suite(c, CHILD(n, 6));
        if (!seq2)
            return NULL;

        return If(expression, seq1, seq2, LINENO(n), n->n_col_offset,
                  c->c_arena);
    }
    else if (s[2] == 'i') {
        int i, n_elif, has_else = 0;
        expr_ty expression;
        asdl_seq *suite_seq;
        asdl_seq *orelse = NULL;
        n_elif = NCH(n) - 4;
        /* must reference the child n_elif+1 since 'else' token is third,
           not fourth, child from the end. */
        if (TYPE(CHILD(n, (n_elif + 1))) == NAME
            && STR(CHILD(n, (n_elif + 1)))[2] == 's') {
            has_else = 1;
            n_elif -= 3;
        }
        n_elif /= 4;

        if (has_else) {
            asdl_seq *suite_seq2;

            orelse = _Py_asdl_seq_new(1, c->c_arena);
            if (!orelse)
                return NULL;
            expression = ast_for_expr(c, CHILD(n, NCH(n) - 6));
            if (!expression)
                return NULL;
            suite_seq = ast_for_suite(c, CHILD(n, NCH(n) - 4));
            if (!suite_seq)
                return NULL;
            suite_seq2 = ast_for_suite(c, CHILD(n, NCH(n) - 1));
            if (!suite_seq2)
                return NULL;

            asdl_seq_SET(orelse, 0,
                         If(expression, suite_seq, suite_seq2,
                            LINENO(CHILD(n, NCH(n) - 6)),
                            CHILD(n, NCH(n) - 6)->n_col_offset,
                            c->c_arena));
            /* the just-created orelse handled the last elif */
            n_elif--;
        }

        for (i = 0; i < n_elif; i++) {
            int off = 5 + (n_elif - i - 1) * 4;
            asdl_seq *newobj = _Py_asdl_seq_new(1, c->c_arena);
            if (!newobj)
                return NULL;
            expression = ast_for_expr(c, CHILD(n, off));
            if (!expression)
                return NULL;
            suite_seq = ast_for_suite(c, CHILD(n, off + 2));
            if (!suite_seq)
                return NULL;

            asdl_seq_SET(newobj, 0,
                         If(expression, suite_seq, orelse,
                            LINENO(CHILD(n, off)),
                            CHILD(n, off)->n_col_offset, c->c_arena));
            orelse = newobj;
        }
        expression = ast_for_expr(c, CHILD(n, 1));
        if (!expression)
            return NULL;
        suite_seq = ast_for_suite(c, CHILD(n, 3));
        if (!suite_seq)
            return NULL;
        return If(expression, suite_seq, orelse,
                  LINENO(n), n->n_col_offset, c->c_arena);
    }

    PyErr_Format(PyExc_SystemError,
                 "unexpected token in 'if' statement: %s", s);
    return NULL;
}

static stmt_ty
ast_for_while_stmt(struct compiling *c, const node *n)
{
    /* while_stmt: 'while' test ':' suite ['else' ':' suite] */
    REQ(n, while_stmt);

    if (NCH(n) == 4) {
        expr_ty expression;
        asdl_seq *suite_seq;

        expression = ast_for_expr(c, CHILD(n, 1));
        if (!expression)
            return NULL;
        suite_seq = ast_for_suite(c, CHILD(n, 3));
        if (!suite_seq)
            return NULL;
        return While(expression, suite_seq, NULL, LINENO(n), n->n_col_offset, c->c_arena);
    }
    else if (NCH(n) == 7) {
        expr_ty expression;
        asdl_seq *seq1, *seq2;

        expression = ast_for_expr(c, CHILD(n, 1));
        if (!expression)
            return NULL;
        seq1 = ast_for_suite(c, CHILD(n, 3));
        if (!seq1)
            return NULL;
        seq2 = ast_for_suite(c, CHILD(n, 6));
        if (!seq2)
            return NULL;

        return While(expression, seq1, seq2, LINENO(n), n->n_col_offset, c->c_arena);
    }

    PyErr_Format(PyExc_SystemError,
                 "wrong number of tokens for 'while' statement: %d",
                 NCH(n));
    return NULL;
}

static stmt_ty
ast_for_for_stmt(struct compiling *c, const node *n, int is_async)
{
    asdl_seq *_target, *seq = NULL, *suite_seq;
    expr_ty expression;
    expr_ty target, first;
    const node *node_target;
    /* for_stmt: 'for' exprlist 'in' testlist ':' suite ['else' ':' suite] */
    REQ(n, for_stmt);

    if (NCH(n) == 9) {
        seq = ast_for_suite(c, CHILD(n, 8));
        if (!seq)
            return NULL;
    }

    node_target = CHILD(n, 1);
    _target = ast_for_exprlist(c, node_target, Store);
    if (!_target)
        return NULL;
    /* Check the # of children rather than the length of _target, since
       for x, in ... has 1 element in _target, but still requires a Tuple. */
    first = (expr_ty)asdl_seq_GET(_target, 0);
    if (NCH(node_target) == 1)
        target = first;
    else
        target = Tuple(_target, Store, first->lineno, first->col_offset, c->c_arena);

    expression = ast_for_testlist(c, CHILD(n, 3));
    if (!expression)
        return NULL;
    suite_seq = ast_for_suite(c, CHILD(n, 5));
    if (!suite_seq)
        return NULL;

    if (is_async)
        return AsyncFor(target, expression, suite_seq, seq,
                        LINENO(n), n->n_col_offset,
                        c->c_arena);
    else
        return For(target, expression, suite_seq, seq,
                   LINENO(n), n->n_col_offset,
                   c->c_arena);
}

static excepthandler_ty
ast_for_except_clause(struct compiling *c, const node *exc, node *body)
{
    /* except_clause: 'except' [test ['as' test]] */
    REQ(exc, except_clause);
    REQ(body, suite);

    if (NCH(exc) == 1) {
        asdl_seq *suite_seq = ast_for_suite(c, body);
        if (!suite_seq)
            return NULL;

        return ExceptHandler(NULL, NULL, suite_seq, LINENO(exc),
                             exc->n_col_offset, c->c_arena);
    }
    else if (NCH(exc) == 2) {
        expr_ty expression;
        asdl_seq *suite_seq;

        expression = ast_for_expr(c, CHILD(exc, 1));
        if (!expression)
            return NULL;
        suite_seq = ast_for_suite(c, body);
        if (!suite_seq)
            return NULL;

        return ExceptHandler(expression, NULL, suite_seq, LINENO(exc),
                             exc->n_col_offset, c->c_arena);
    }
    else if (NCH(exc) == 4) {
        asdl_seq *suite_seq;
        expr_ty expression;
        identifier e = NEW_IDENTIFIER(CHILD(exc, 3));
        if (!e)
            return NULL;
        if (forbidden_name(c, e, CHILD(exc, 3), 0))
            return NULL;
        expression = ast_for_expr(c, CHILD(exc, 1));
        if (!expression)
            return NULL;
        suite_seq = ast_for_suite(c, body);
        if (!suite_seq)
            return NULL;

        return ExceptHandler(expression, e, suite_seq, LINENO(exc),
                             exc->n_col_offset, c->c_arena);
    }

    PyErr_Format(PyExc_SystemError,
                 "wrong number of children for 'except' clause: %d",
                 NCH(exc));
    return NULL;
}

static stmt_ty
ast_for_try_stmt(struct compiling *c, const node *n)
{
    const int nch = NCH(n);
    int n_except = (nch - 3)/3;
    asdl_seq *body, *handlers = NULL, *orelse = NULL, *finally = NULL;

    REQ(n, try_stmt);

    body = ast_for_suite(c, CHILD(n, 2));
    if (body == NULL)
        return NULL;

    if (TYPE(CHILD(n, nch - 3)) == NAME) {
        if (strcmp(STR(CHILD(n, nch - 3)), "finally") == 0) {
            if (nch >= 9 && TYPE(CHILD(n, nch - 6)) == NAME) {
                /* we can assume it's an "else",
                   because nch >= 9 for try-else-finally and
                   it would otherwise have a type of except_clause */
                orelse = ast_for_suite(c, CHILD(n, nch - 4));
                if (orelse == NULL)
                    return NULL;
                n_except--;
            }

            finally = ast_for_suite(c, CHILD(n, nch - 1));
            if (finally == NULL)
                return NULL;
            n_except--;
        }
        else {
            /* we can assume it's an "else",
               otherwise it would have a type of except_clause */
            orelse = ast_for_suite(c, CHILD(n, nch - 1));
            if (orelse == NULL)
                return NULL;
            n_except--;
        }
    }
    else if (TYPE(CHILD(n, nch - 3)) != except_clause) {
        ast_error(c, n, "malformed 'try' statement");
        return NULL;
    }

    if (n_except > 0) {
        int i;
        /* process except statements to create a try ... except */
        handlers = _Py_asdl_seq_new(n_except, c->c_arena);
        if (handlers == NULL)
            return NULL;

        for (i = 0; i < n_except; i++) {
            excepthandler_ty e = ast_for_except_clause(c, CHILD(n, 3 + i * 3),
                                                       CHILD(n, 5 + i * 3));
            if (!e)
                return NULL;
            asdl_seq_SET(handlers, i, e);
        }
    }

    assert(finally != NULL || asdl_seq_LEN(handlers));
    return Try(body, handlers, orelse, finally, LINENO(n), n->n_col_offset, c->c_arena);
}

/* with_item: test ['as' expr] */
static withitem_ty
ast_for_with_item(struct compiling *c, const node *n)
{
    expr_ty context_expr, optional_vars = NULL;

    REQ(n, with_item);
    context_expr = ast_for_expr(c, CHILD(n, 0));
    if (!context_expr)
        return NULL;
    if (NCH(n) == 3) {
        optional_vars = ast_for_expr(c, CHILD(n, 2));

        if (!optional_vars) {
            return NULL;
        }
        if (!set_context(c, optional_vars, Store, n)) {
            return NULL;
        }
    }

    return withitem(context_expr, optional_vars, c->c_arena);
}

/* with_stmt: 'with' with_item (',' with_item)* ':' suite */
static stmt_ty
ast_for_with_stmt(struct compiling *c, const node *n, int is_async)
{
    int i, n_items;
    asdl_seq *items, *body;

    REQ(n, with_stmt);

    n_items = (NCH(n) - 2) / 2;
    items = _Py_asdl_seq_new(n_items, c->c_arena);
    if (!items)
        return NULL;
    for (i = 1; i < NCH(n) - 2; i += 2) {
        withitem_ty item = ast_for_with_item(c, CHILD(n, i));
        if (!item)
            return NULL;
        asdl_seq_SET(items, (i - 1) / 2, item);
    }

    body = ast_for_suite(c, CHILD(n, NCH(n) - 1));
    if (!body)
        return NULL;

    if (is_async)
        return AsyncWith(items, body, LINENO(n), n->n_col_offset, c->c_arena);
    else
        return With(items, body, LINENO(n), n->n_col_offset, c->c_arena);
}

static stmt_ty
ast_for_classdef(struct compiling *c, const node *n, asdl_seq *decorator_seq)
{
    /* classdef: 'class' NAME ['(' arglist ')'] ':' suite */
    PyObject *classname;
    asdl_seq *s;
    expr_ty call;

    REQ(n, classdef);

    if (NCH(n) == 4) { /* class NAME ':' suite */
        s = ast_for_suite(c, CHILD(n, 3));
        if (!s)
            return NULL;
        classname = NEW_IDENTIFIER(CHILD(n, 1));
        if (!classname)
            return NULL;
        if (forbidden_name(c, classname, CHILD(n, 3), 0))
            return NULL;
        return ClassDef(classname, NULL, NULL, s, decorator_seq, LINENO(n),
                        n->n_col_offset, c->c_arena);
    }

    if (TYPE(CHILD(n, 3)) == RPAR) { /* class NAME '(' ')' ':' suite */
        s = ast_for_suite(c, CHILD(n,5));
        if (!s)
            return NULL;
        classname = NEW_IDENTIFIER(CHILD(n, 1));
        if (!classname)
            return NULL;
        if (forbidden_name(c, classname, CHILD(n, 3), 0))
            return NULL;
        return ClassDef(classname, NULL, NULL, s, decorator_seq, LINENO(n),
                        n->n_col_offset, c->c_arena);
    }

    /* class NAME '(' arglist ')' ':' suite */
    /* build up a fake Call node so we can extract its pieces */
    {
        PyObject *dummy_name;
        expr_ty dummy;
        dummy_name = NEW_IDENTIFIER(CHILD(n, 1));
        if (!dummy_name)
            return NULL;
        dummy = Name(dummy_name, Load, LINENO(n), n->n_col_offset, c->c_arena);
        call = ast_for_call(c, CHILD(n, 3), dummy);
        if (!call)
            return NULL;
    }
    s = ast_for_suite(c, CHILD(n, 6));
    if (!s)
        return NULL;
    classname = NEW_IDENTIFIER(CHILD(n, 1));
    if (!classname)
        return NULL;
    if (forbidden_name(c, classname, CHILD(n, 1), 0))
        return NULL;

    return ClassDef(classname, call->v.Call.args, call->v.Call.keywords, s,
                    decorator_seq, LINENO(n), n->n_col_offset, c->c_arena);
}

static stmt_ty
ast_for_stmt(struct compiling *c, const node *n)
{
    if (TYPE(n) == stmt) {
        assert(NCH(n) == 1);
        n = CHILD(n, 0);
    }
    if (TYPE(n) == simple_stmt) {
        assert(num_stmts(n) == 1);
        n = CHILD(n, 0);
    }
    if (TYPE(n) == small_stmt) {
        n = CHILD(n, 0);
        /* small_stmt: expr_stmt | del_stmt | pass_stmt | flow_stmt
                  | import_stmt | global_stmt | nonlocal_stmt | assert_stmt
        */
        switch (TYPE(n)) {
            case expr_stmt:
                return ast_for_expr_stmt(c, n);
            case del_stmt:
                return ast_for_del_stmt(c, n);
            case pass_stmt:
                return Pass(LINENO(n), n->n_col_offset, c->c_arena);
            case flow_stmt:
                return ast_for_flow_stmt(c, n);
            case import_stmt:
                return ast_for_import_stmt(c, n);
            case global_stmt:
                return ast_for_global_stmt(c, n);
            case nonlocal_stmt:
                return ast_for_nonlocal_stmt(c, n);
            case assert_stmt:
                return ast_for_assert_stmt(c, n);
            default:
                PyErr_Format(PyExc_SystemError,
                             "unhandled small_stmt: TYPE=%d NCH=%d\n",
                             TYPE(n), NCH(n));
                return NULL;
        }
    }
    else {
        /* compound_stmt: if_stmt | while_stmt | for_stmt | try_stmt
                        | funcdef | classdef | decorated | async_stmt
        */
        node *ch = CHILD(n, 0);
        REQ(n, compound_stmt);
        switch (TYPE(ch)) {
            case if_stmt:
                return ast_for_if_stmt(c, ch);
            case while_stmt:
                return ast_for_while_stmt(c, ch);
            case for_stmt:
                return ast_for_for_stmt(c, ch, 0);
            case try_stmt:
                return ast_for_try_stmt(c, ch);
            case with_stmt:
                return ast_for_with_stmt(c, ch, 0);
            case funcdef:
                return ast_for_funcdef(c, ch, NULL);
            case classdef:
                return ast_for_classdef(c, ch, NULL);
            case decorated:
                return ast_for_decorated(c, ch);
            case async_stmt:
                return ast_for_async_stmt(c, ch);
            default:
                PyErr_Format(PyExc_SystemError,
                             "unhandled small_stmt: TYPE=%d NCH=%d\n",
                             TYPE(n), NCH(n));
                return NULL;
        }
    }
}

static PyObject *
parsenumber(struct compiling *c, const char *s)
{
    const char *end;
    long x;
    double dx;
    Py_complex compl;
    int imflag;

    assert(s != NULL);
    errno = 0;
    end = s + strlen(s) - 1;
    imflag = *end == 'j' || *end == 'J';
    if (s[0] == '0') {
        x = (long) PyOS_strtoul(s, (char **)&end, 0);
        if (x < 0 && errno == 0) {
            return PyLong_FromString(s, (char **)0, 0);
        }
    }
    else
        x = PyOS_strtol(s, (char **)&end, 0);
    if (*end == '\0') {
        if (errno != 0)
            return PyLong_FromString(s, (char **)0, 0);
        return PyLong_FromLong(x);
    }
    /* XXX Huge floats may silently fail */
    if (imflag) {
        compl.real = 0.;
        compl.imag = PyOS_string_to_double(s, (char **)&end, NULL);
        if (compl.imag == -1.0 && PyErr_Occurred())
            return NULL;
        return PyComplex_FromCComplex(compl);
    }
    else
    {
        dx = PyOS_string_to_double(s, NULL, NULL);
        if (dx == -1.0 && PyErr_Occurred())
            return NULL;
        return PyFloat_FromDouble(dx);
    }
}

static PyObject *
decode_utf8(struct compiling *c, const char **sPtr, const char *end)
{
    const char *s, *t;
    t = s = *sPtr;
    /* while (s < end && *s != '\\') s++; */ /* inefficient for u".." */
    while (s < end && (*s & 0x80)) s++;
    *sPtr = s;
    return PyUnicode_DecodeUTF8(t, s - t, NULL);
}

static PyObject *
decode_unicode(struct compiling *c, const char *s, size_t len, const char *encoding)
{
    PyObject *v, *u;
    char *buf;
    char *p;
    const char *end;

    if (encoding == NULL) {
        u = NULL;
    } else {
        /* check for integer overflow */
        if (len > PY_SIZE_MAX / 6)
            return NULL;
        /* "ä" (2 bytes) may become "\U000000E4" (10 bytes), or 1:5
           "\ä" (3 bytes) may become "\u005c\U000000E4" (16 bytes), or ~1:6 */
        u = PyBytes_FromStringAndSize((char *)NULL, len * 6);
        if (u == NULL)
            return NULL;
        p = buf = PyBytes_AsString(u);
        end = s + len;
        while (s < end) {
            if (*s == '\\') {
                *p++ = *s++;
                if (*s & 0x80) {
                    strcpy(p, "u005c");
                    p += 5;
                }
            }
            if (*s & 0x80) { /* XXX inefficient */
                PyObject *w;
                int kind;
                void *data;
                Py_ssize_t len, i;
                w = decode_utf8(c, &s, end);
                if (w == NULL) {
                    Py_DECREF(u);
                    return NULL;
                }
                kind = PyUnicode_KIND(w);
                data = PyUnicode_DATA(w);
                len = PyUnicode_GET_LENGTH(w);
                for (i = 0; i < len; i++) {
                    Py_UCS4 chr = PyUnicode_READ(kind, data, i);
                    sprintf(p, "\\U%08x", chr);
                    p += 10;
                }
                /* Should be impossible to overflow */
                assert(p - buf <= Py_SIZE(u));
                Py_DECREF(w);
            } else {
                *p++ = *s++;
            }
        }
        len = p - buf;
        s = buf;
    }
    v = PyUnicode_DecodeUnicodeEscape(s, len, NULL);
    Py_XDECREF(u);
    return v;
}

/* Compile this expression in to an expr_ty. We know that we can
   temporarily modify the character before the start of this string
   (it's '{'), and we know we can temporarily modify the character
   after this string (it is a '}').  Leverage this to create a
   sub-string with enough room for us to add parens around the
   expression. This is to allow strings with embedded newlines, for
   example. */
static expr_ty
fstring_compile_expr(PyObject *str, Py_ssize_t expr_start,
                     Py_ssize_t expr_end, struct compiling *c, const node *n)

{
    PyCompilerFlags cf;
    mod_ty mod;
    char *utf_expr;
    Py_ssize_t i;
    Py_UCS4 end_ch = -1;
    int all_whitespace;
    PyObject *sub = NULL;

    /* We only decref sub if we allocated it with a PyUnicode_Substring.
       decref_sub records that. */
    int decref_sub = 0;

    assert(str);

    assert(expr_start >= 0 && expr_start < PyUnicode_GET_LENGTH(str));
    assert(expr_end >= 0 && expr_end < PyUnicode_GET_LENGTH(str));
    assert(expr_end >= expr_start);

    /* There has to be at least on character on each side of the
       expression inside this str. This will have been caught before
       we're called. */
    assert(expr_start >= 1);
    assert(expr_end <= PyUnicode_GET_LENGTH(str)-1);

    /* If the substring is all whitespace, it's an error. We need to
        catch this here, and not when we call PyParser_ASTFromString,
        because turning the expression '' in to '()' would go from
        being invalid to valid. */
    /* Note that this code says an empty string is all
        whitespace. That's important. There's a test for it: f'{}'. */
    all_whitespace = 1;
    for (i = expr_start; i < expr_end; i++) {
        if (!Py_UNICODE_ISSPACE(PyUnicode_READ_CHAR(str, i))) {
            all_whitespace = 0;
            break;
        }
    }
    if (all_whitespace) {
        ast_error(c, n, "f-string: empty expression not allowed");
        goto error;
    }

    /* If the substring will be the entire source string, we can't use
        PyUnicode_Substring, since it will return another reference to
        our original string. Because we're modifying the string in
        place, that's a no-no. So, detect that case and just use our
        string directly. */

    if (expr_start-1 == 0 && expr_end+1 == PyUnicode_GET_LENGTH(str)) {
        /* If str is well formed, then the first and last chars must
           be '{' and '}', respectively. But, if there's a syntax
           error, for example f'{3!', then the last char won't be a
           closing brace. So, remember the last character we read in
           order for us to restore it. */
        end_ch = PyUnicode_ReadChar(str, expr_end-expr_start+1);
        assert(end_ch != (Py_UCS4)-1);

        /* In all cases, however, start_ch must be '{'. */
        assert(PyUnicode_ReadChar(str, 0) == '{');

        sub = str;
    } else {
        /* Create a substring object. It must be a new object, with
           refcount==1, so that we can modify it. */
        sub = PyUnicode_Substring(str, expr_start-1, expr_end+1);
        if (!sub)
            goto error;
        assert(sub != str);  /* Make sure it's a new string. */
        decref_sub = 1;      /* Remember to deallocate it on error. */
    }

    /* Put () around the expression. */
    if (PyUnicode_WriteChar(sub, 0, '(') < 0 ||
        PyUnicode_WriteChar(sub, expr_end-expr_start+1, ')') < 0)
        goto error;

    /* No need to free the memory returned here: it's managed by the
       string. */
    utf_expr = PyUnicode_AsUTF8(sub);
    if (!utf_expr)
        goto error;

    cf.cf_flags = PyCF_ONLY_AST;
    mod = PyParser_ASTFromString(utf_expr, "<fstring>",
                                 Py_eval_input, &cf, c->c_arena);
    if (!mod)
        goto error;

    if (sub != str)
        /* Clear instead of decref in case we ever modify this code to change
           the error handling: this is safest because the XDECREF won't try
           and decref it when it's NULL. */
        /* No need to restore the chars in sub, since we know it's getting
           ready to get deleted (refcount must be 1, since we got a new string
           in PyUnicode_Substring). */
        Py_CLEAR(sub);
    else {
        assert(!decref_sub);
        assert(end_ch != (Py_UCS4)-1);
        /* Restore str, which we earlier modified directly. */
        if (PyUnicode_WriteChar(str, 0, '{') < 0 ||
            PyUnicode_WriteChar(str, expr_end-expr_start+1, end_ch) < 0)
            goto error;
    }
    return mod->v.Expression.body;

error:
    /* Only decref sub if it was the result of a call to SubString. */
    if (decref_sub)
        Py_XDECREF(sub);

    if (end_ch != (Py_UCS4)-1) {
        /* We only get here if we modified str. Make sure that's the
           case: str will be equal to sub. */
        if (str == sub) {
            /* Don't check the error, because we've already set the
               error state (that's why we're in 'error', after
               all). */
            PyUnicode_WriteChar(str, 0, '{');
            PyUnicode_WriteChar(str, expr_end-expr_start+1, end_ch);
        }
    }
    return NULL;
}

/* Return -1 on error.

   Return 0 if we reached the end of the literal.

   Return 1 if we haven't reached the end of the literal, but we want
   the caller to process the literal up to this point. Used for
   doubled braces.
*/
static int
fstring_find_literal(PyObject *str, Py_ssize_t *ofs, PyObject **literal,
                     int recurse_lvl, struct compiling *c, const node *n)
{
    /* Get any literal string. It ends when we hit an un-doubled brace, or the
       end of the string. */

    Py_ssize_t literal_start, literal_end;
    int result = 0;

    enum PyUnicode_Kind kind = PyUnicode_KIND(str);
    void *data = PyUnicode_DATA(str);

    assert(*literal == NULL);

    literal_start = *ofs;
    for (; *ofs < PyUnicode_GET_LENGTH(str); *ofs += 1) {
        Py_UCS4 ch = PyUnicode_READ(kind, data, *ofs);
        if (ch == '{' || ch == '}') {
            /* Check for doubled braces, but only at the top level. If
               we checked at every level, then f'{0:{3}}' would fail
               with the two closing braces. */
            if (recurse_lvl == 0) {
                if (*ofs + 1 < PyUnicode_GET_LENGTH(str) &&
                    PyUnicode_READ(kind, data, *ofs + 1) == ch) {
                    /* We're going to tell the caller that the literal ends
                       here, but that they should continue scanning. But also
                       skip over the second brace when we resume scanning. */
                    literal_end = *ofs + 1;
                    *ofs += 2;
                    result = 1;
                    goto done;
                }

                /* Where a single '{' is the start of a new expression, a
                   single '}' is not allowed. */
                if (ch == '}') {
                    ast_error(c, n, "f-string: single '}' is not allowed");
                    return -1;
                }
            }

            /* We're either at a '{', which means we're starting another
               expression; or a '}', which means we're at the end of this
               f-string (for a nested format_spec). */
            break;
        }
    }
    literal_end = *ofs;

    assert(*ofs == PyUnicode_GET_LENGTH(str) ||
           PyUnicode_READ(kind, data, *ofs) == '{' ||
           PyUnicode_READ(kind, data, *ofs) == '}');
done:
    if (literal_start != literal_end) {
        *literal = PyUnicode_Substring(str, literal_start, literal_end);
        if (!*literal)
            return -1;
    }

    return result;
}

/* Forward declaration because parsing is recursive. */
static expr_ty
fstring_parse(PyObject *str, Py_ssize_t *ofs, int recurse_lvl,
              struct compiling *c, const node *n);

/* Parse the f-string str, starting at ofs. We know *ofs starts an
   expression (so it must be a '{'). Returns the FormattedValue node,
   which includes the expression, conversion character, and
   format_spec expression.

   Note that I don't do a perfect job here: I don't make sure that a
   closing brace doesn't match an opening paren, for example. It
   doesn't need to error on all invalid expressions, just correctly
   find the end of all valid ones. Any errors inside the expression
   will be caught when we parse it later. */
static int
fstring_find_expr(PyObject *str, Py_ssize_t *ofs, int recurse_lvl,
                  expr_ty *expression, struct compiling *c, const node *n)
{
    /* Return -1 on error, else 0. */

    Py_ssize_t expr_start;
    Py_ssize_t expr_end;
    expr_ty simple_expression;
    expr_ty format_spec = NULL; /* Optional format specifier. */
    Py_UCS4 conversion = -1; /* The conversion char. -1 if not specified. */

    enum PyUnicode_Kind kind = PyUnicode_KIND(str);
    void *data = PyUnicode_DATA(str);

    /* 0 if we're not in a string, else the quote char we're trying to
       match (single or double quote). */
    Py_UCS4 quote_char = 0;

    /* If we're inside a string, 1=normal, 3=triple-quoted. */
    int string_type = 0;

    /* Keep track of nesting level for braces/parens/brackets in
       expressions. */
    Py_ssize_t nested_depth = 0;

    /* Can only nest one level deep. */
    if (recurse_lvl >= 2) {
        ast_error(c, n, "f-string: expressions nested too deeply");
        return -1;
    }

    /* The first char must be a left brace, or we wouldn't have gotten
       here. Skip over it. */
    assert(PyUnicode_READ(kind, data, *ofs) == '{');
    *ofs += 1;

    expr_start = *ofs;
    for (; *ofs < PyUnicode_GET_LENGTH(str); *ofs += 1) {
        Py_UCS4 ch;

        /* Loop invariants. */
        assert(nested_depth >= 0);
        assert(*ofs >= expr_start);
        if (quote_char)
            assert(string_type == 1 || string_type == 3);
        else
            assert(string_type == 0);

        ch = PyUnicode_READ(kind, data, *ofs);
        if (quote_char) {
            /* We're inside a string. See if we're at the end. */
            /* This code needs to implement the same non-error logic
               as tok_get from tokenizer.c, at the letter_quote
               label. To actually share that code would be a
               nightmare. But, it's unlikely to change and is small,
               so duplicate it here. Note we don't need to catch all
               of the errors, since they'll be caught when parsing the
               expression. We just need to match the non-error
               cases. Thus we can ignore \n in single-quoted strings,
               for example. Or non-terminated strings. */
            if (ch == quote_char) {
                /* Does this match the string_type (single or triple
                   quoted)? */
                if (string_type == 3) {
                    if (*ofs+2 < PyUnicode_GET_LENGTH(str) &&
                        PyUnicode_READ(kind, data, *ofs+1) == ch &&
                        PyUnicode_READ(kind, data, *ofs+2) == ch) {
                        /* We're at the end of a triple quoted string. */
                        *ofs += 2;
                        string_type = 0;
                        quote_char = 0;
                        continue;
                    }
                } else {
                    /* We're at the end of a normal string. */
                    quote_char = 0;
                    string_type = 0;
                    continue;
                }
            }
            /* We're inside a string, and not finished with the
               string. If this is a backslash, skip the next char (it
               might be an end quote that needs skipping). Otherwise,
               just consume this character normally. */
            if (ch == '\\' && *ofs+1 < PyUnicode_GET_LENGTH(str)) {
                /* Just skip the next char, whatever it is. */
                *ofs += 1;
            }
        } else if (ch == '\'' || ch == '"') {
            /* Is this a triple quoted string? */
            if (*ofs+2 < PyUnicode_GET_LENGTH(str) &&
                PyUnicode_READ(kind, data, *ofs+1) == ch &&
                PyUnicode_READ(kind, data, *ofs+2) == ch) {
                string_type = 3;
                *ofs += 2;
            } else {
                /* Start of a normal string. */
                string_type = 1;
            }
            /* Start looking for the end of the string. */
            quote_char = ch;
        } else if (ch == '[' || ch == '{' || ch == '(') {
            nested_depth++;
        } else if (nested_depth != 0 &&
                   (ch == ']' || ch == '}' || ch == ')')) {
            nested_depth--;
        } else if (ch == '#') {
            /* Error: can't include a comment character, inside parens
               or not. */
            ast_error(c, n, "f-string cannot include '#'");
            return -1;
        } else if (nested_depth == 0 &&
                   (ch == '!' || ch == ':' || ch == '}')) {
            /* First, test for the special case of "!=". Since '=' is
               not an allowed conversion character, nothing is lost in
               this test. */
            if (ch == '!' && *ofs+1 < PyUnicode_GET_LENGTH(str) &&
                  PyUnicode_READ(kind, data, *ofs+1) == '=')
                /* This isn't a conversion character, just continue. */
                continue;

            /* Normal way out of this loop. */
            break;
        } else {
            /* Just consume this char and loop around. */
        }
    }
    expr_end = *ofs;
    /* If we leave this loop in a string or with mismatched parens, we
       don't care. We'll get a syntax error when compiling the
       expression. But, we can produce a better error message, so
       let's just do that.*/
    if (quote_char) {
        ast_error(c, n, "f-string: unterminated string");
        return -1;
    }
    if (nested_depth) {
        ast_error(c, n, "f-string: mismatched '(', '{', or '['");
        return -1;
    }

    if (*ofs >= PyUnicode_GET_LENGTH(str))
        goto unexpected_end_of_string;

    /* Compile the expression as soon as possible, so we show errors
       related to the expression before errors related to the
       conversion or format_spec. */
    simple_expression = fstring_compile_expr(str, expr_start, expr_end, c, n);
    if (!simple_expression)
        return -1;

    /* Check for a conversion char, if present. */
    if (PyUnicode_READ(kind, data, *ofs) == '!') {
        *ofs += 1;
        if (*ofs >= PyUnicode_GET_LENGTH(str))
            goto unexpected_end_of_string;

        conversion = PyUnicode_READ(kind, data, *ofs);
        *ofs += 1;

        /* Validate the conversion. */
        if (!(conversion == 's' || conversion == 'r'
              || conversion == 'a')) {
            ast_error(c, n, "f-string: invalid conversion character: "
                            "expected 's', 'r', or 'a'");
            return -1;
        }
    }

    /* Check for the format spec, if present. */
    if (*ofs >= PyUnicode_GET_LENGTH(str))
        goto unexpected_end_of_string;
    if (PyUnicode_READ(kind, data, *ofs) == ':') {
        *ofs += 1;
        if (*ofs >= PyUnicode_GET_LENGTH(str))
            goto unexpected_end_of_string;

        /* Parse the format spec. */
        format_spec = fstring_parse(str, ofs, recurse_lvl+1, c, n);
        if (!format_spec)
            return -1;
    }

    if (*ofs >= PyUnicode_GET_LENGTH(str) ||
          PyUnicode_READ(kind, data, *ofs) != '}')
        goto unexpected_end_of_string;

    /* We're at a right brace. Consume it. */
    assert(*ofs < PyUnicode_GET_LENGTH(str));
    assert(PyUnicode_READ(kind, data, *ofs) == '}');
    *ofs += 1;

    /* And now create the FormattedValue node that represents this entire
       expression with the conversion and format spec. */
    *expression = FormattedValue(simple_expression, (int)conversion,
                                 format_spec, LINENO(n), n->n_col_offset,
                                 c->c_arena);
    if (!*expression)
        return -1;

    return 0;

unexpected_end_of_string:
    ast_error(c, n, "f-string: expecting '}'");
    return -1;
}

/* Return -1 on error.

   Return 0 if we have a literal (possible zero length) and an
   expression (zero length if at the end of the string.

   Return 1 if we have a literal, but no expression, and we want the
   caller to call us again. This is used to deal with doubled
   braces.

   When called multiple times on the string 'a{{b{0}c', this function
   will return:

   1. the literal 'a{' with no expression, and a return value
      of 1. Despite the fact that there's no expression, the return
      value of 1 means we're not finished yet.

   2. the literal 'b' and the expression '0', with a return value of
      0. The fact that there's an expression means we're not finished.

   3. literal 'c' with no expression and a return value of 0. The
      combination of the return value of 0 with no expression means
      we're finished.
*/
static int
fstring_find_literal_and_expr(PyObject *str, Py_ssize_t *ofs, int recurse_lvl,
                              PyObject **literal, expr_ty *expression,
                              struct compiling *c, const node *n)
{
    int result;

    assert(*literal == NULL && *expression == NULL);

    /* Get any literal string. */
    result = fstring_find_literal(str, ofs, literal, recurse_lvl, c, n);
    if (result < 0)
        goto error;

    assert(result == 0 || result == 1);

    if (result == 1)
        /* We have a literal, but don't look at the expression. */
        return 1;

    assert(*ofs <= PyUnicode_GET_LENGTH(str));

    if (*ofs >= PyUnicode_GET_LENGTH(str) ||
        PyUnicode_READ_CHAR(str, *ofs) == '}')
        /* We're at the end of the string or the end of a nested
           f-string: no expression. The top-level error case where we
           expect to be at the end of the string but we're at a '}' is
           handled later. */
        return 0;

    /* We must now be the start of an expression, on a '{'. */
    assert(*ofs < PyUnicode_GET_LENGTH(str) &&
           PyUnicode_READ_CHAR(str, *ofs) == '{');

    if (fstring_find_expr(str, ofs, recurse_lvl, expression, c, n) < 0)
        goto error;

    return 0;

error:
    Py_XDECREF(*literal);
    *literal = NULL;
    return -1;
}

#define EXPRLIST_N_CACHED  64

typedef struct {
    /* Incrementally build an array of expr_ty, so be used in an
       asdl_seq. Cache some small but reasonably sized number of
       expr_ty's, and then after that start dynamically allocating,
       doubling the number allocated each time. Note that the f-string
       f'{0}a{1}' contains 3 expr_ty's: 2 FormattedValue's, and one
       Str for the literal 'a'. So you add expr_ty's about twice as
       fast as you add exressions in an f-string. */

    Py_ssize_t allocated;  /* Number we've allocated. */
    Py_ssize_t size;       /* Number we've used. */
    expr_ty    *p;         /* Pointer to the memory we're actually
                              using. Will point to 'data' until we
                              start dynamically allocating. */
    expr_ty    data[EXPRLIST_N_CACHED];
} ExprList;

#ifdef NDEBUG
#define ExprList_check_invariants(l)
#else
static void
ExprList_check_invariants(ExprList *l)
{
    /* Check our invariants. Make sure this object is "live", and
       hasn't been deallocated. */
    assert(l->size >= 0);
    assert(l->p != NULL);
    if (l->size <= EXPRLIST_N_CACHED)
        assert(l->data == l->p);
}
#endif

static void
ExprList_Init(ExprList *l)
{
    l->allocated = EXPRLIST_N_CACHED;
    l->size = 0;

    /* Until we start allocating dynamically, p points to data. */
    l->p = l->data;

    ExprList_check_invariants(l);
}

static int
ExprList_Append(ExprList *l, expr_ty exp)
{
    ExprList_check_invariants(l);
    if (l->size >= l->allocated) {
        /* We need to alloc (or realloc) the memory. */
        Py_ssize_t new_size = l->allocated * 2;

        /* See if we've ever allocated anything dynamically. */
        if (l->p == l->data) {
            Py_ssize_t i;
            /* We're still using the cached data. Switch to
               alloc-ing. */
            l->p = PyMem_RawMalloc(sizeof(expr_ty) * new_size);
            if (!l->p)
                return -1;
            /* Copy the cached data into the new buffer. */
            for (i = 0; i < l->size; i++)
                l->p[i] = l->data[i];
        } else {
            /* Just realloc. */
            expr_ty *tmp = PyMem_RawRealloc(l->p, sizeof(expr_ty) * new_size);
            if (!tmp) {
                PyMem_RawFree(l->p);
                l->p = NULL;
                return -1;
            }
            l->p = tmp;
        }

        l->allocated = new_size;
        assert(l->allocated == 2 * l->size);
    }

    l->p[l->size++] = exp;

    ExprList_check_invariants(l);
    return 0;
}

static void
ExprList_Dealloc(ExprList *l)
{
    ExprList_check_invariants(l);

    /* If there's been an error, or we've never dynamically allocated,
       do nothing. */
    if (!l->p || l->p == l->data) {
        /* Do nothing. */
    } else {
        /* We have dynamically allocated. Free the memory. */
        PyMem_RawFree(l->p);
    }
    l->p = NULL;
    l->size = -1;
}

static asdl_seq *
ExprList_Finish(ExprList *l, PyArena *arena)
{
    asdl_seq *seq;

    ExprList_check_invariants(l);

    /* Allocate the asdl_seq and copy the expressions in to it. */
    seq = _Py_asdl_seq_new(l->size, arena);
    if (seq) {
        Py_ssize_t i;
        for (i = 0; i < l->size; i++)
            asdl_seq_SET(seq, i, l->p[i]);
    }
    ExprList_Dealloc(l);
    return seq;
}

/* The FstringParser is designed to add a mix of strings and
   f-strings, and concat them together as needed. Ultimately, it
   generates an expr_ty. */
typedef struct {
    PyObject *last_str;
    ExprList expr_list;
} FstringParser;

#ifdef NDEBUG
#define FstringParser_check_invariants(state)
#else
static void
FstringParser_check_invariants(FstringParser *state)
{
    if (state->last_str)
        assert(PyUnicode_CheckExact(state->last_str));
    ExprList_check_invariants(&state->expr_list);
}
#endif

static void
FstringParser_Init(FstringParser *state)
{
    state->last_str = NULL;
    ExprList_Init(&state->expr_list);
    FstringParser_check_invariants(state);
}

static void
FstringParser_Dealloc(FstringParser *state)
{
    FstringParser_check_invariants(state);

    Py_XDECREF(state->last_str);
    ExprList_Dealloc(&state->expr_list);
}

/* Make a Str node, but decref the PyUnicode object being added. */
static expr_ty
make_str_node_and_del(PyObject **str, struct compiling *c, const node* n)
{
    PyObject *s = *str;
    *str = NULL;
    assert(PyUnicode_CheckExact(s));
    if (PyArena_AddPyObject(c->c_arena, s) < 0) {
        Py_DECREF(s);
        return NULL;
    }
    return Str(s, LINENO(n), n->n_col_offset, c->c_arena);
}

/* Add a non-f-string (that is, a regular literal string). str is
   decref'd. */
static int
FstringParser_ConcatAndDel(FstringParser *state, PyObject *str)
{
    FstringParser_check_invariants(state);

    assert(PyUnicode_CheckExact(str));

    if (PyUnicode_GET_LENGTH(str) == 0) {
        Py_DECREF(str);
        return 0;
    }

    if (!state->last_str) {
        /* We didn't have a string before, so just remember this one. */
        state->last_str = str;
    } else {
        /* Concatenate this with the previous string. */
        PyObject *temp = PyUnicode_Concat(state->last_str, str);
        Py_DECREF(state->last_str);
        Py_DECREF(str);
        state->last_str = temp;
        if (!temp)
            return -1;
    }
    FstringParser_check_invariants(state);
    return 0;
}

/* Parse an f-string. The f-string is in str, starting at ofs, with no 'f'
   or quotes. str is not decref'd, since we don't know if it's used elsewhere.
   And if we're only looking at a part of a string, then decref'ing is
   definitely not the right thing to do! */
static int
FstringParser_ConcatFstring(FstringParser *state, PyObject *str,
                            Py_ssize_t *ofs, int recurse_lvl,
                            struct compiling *c, const node *n)
{
    FstringParser_check_invariants(state);

    /* Parse the f-string. */
    while (1) {
        PyObject *literal = NULL;
        expr_ty expression = NULL;

        /* If there's a zero length literal in front of the
           expression, literal will be NULL. If we're at the end of
           the f-string, expression will be NULL (unless result == 1,
           see below). */
        int result = fstring_find_literal_and_expr(str, ofs, recurse_lvl,
                                                   &literal, &expression,
                                                   c, n);
        if (result < 0)
            return -1;

        /* Add the literal, if any. */
        if (!literal) {
            /* Do nothing. Just leave last_str alone (and possibly
               NULL). */
        } else if (!state->last_str) {
            state->last_str = literal;
            literal = NULL;
        } else {
            /* We have a literal, concatenate it. */
            assert(PyUnicode_GET_LENGTH(literal) != 0);
            if (FstringParser_ConcatAndDel(state, literal) < 0)
                return -1;
            literal = NULL;
        }
        assert(!state->last_str ||
               PyUnicode_GET_LENGTH(state->last_str) != 0);

        /* We've dealt with the literal now. It can't be leaked on further
           errors. */
        assert(literal == NULL);

        /* See if we should just loop around to get the next literal
           and expression, while ignoring the expression this
           time. This is used for un-doubling braces, as an
           optimization. */
        if (result == 1)
            continue;

        if (!expression)
            /* We're done with this f-string. */
            break;

        /* We know we have an expression. Convert any existing string
           to a Str node. */
        if (!state->last_str) {
            /* Do nothing. No previous literal. */
        } else {
            /* Convert the existing last_str literal to a Str node. */
            expr_ty str = make_str_node_and_del(&state->last_str, c, n);
            if (!str || ExprList_Append(&state->expr_list, str) < 0)
                return -1;
        }

        if (ExprList_Append(&state->expr_list, expression) < 0)
            return -1;
    }

    assert(*ofs <= PyUnicode_GET_LENGTH(str));

    /* If recurse_lvl is zero, then we must be at the end of the
       string. Otherwise, we must be at a right brace. */

    if (recurse_lvl == 0 && *ofs < PyUnicode_GET_LENGTH(str)) {
        ast_error(c, n, "f-string: unexpected end of string");
        return -1;
    }
    if (recurse_lvl != 0 && PyUnicode_READ_CHAR(str, *ofs) != '}') {
        ast_error(c, n, "f-string: expecting '}'");
        return -1;
    }

    FstringParser_check_invariants(state);
    return 0;
}

/* Convert the partial state reflected in last_str and expr_list to an
   expr_ty. The expr_ty can be a Str, or a JoinedStr. */
static expr_ty
FstringParser_Finish(FstringParser *state, struct compiling *c,
                     const node *n)
{
    asdl_seq *seq;

    FstringParser_check_invariants(state);

    /* If we're just a constant string with no expressions, return
       that. */
    if(state->expr_list.size == 0) {
        if (!state->last_str) {
            /* Create a zero length string. */
            state->last_str = PyUnicode_FromStringAndSize(NULL, 0);
            if (!state->last_str)
                goto error;
        }
        return make_str_node_and_del(&state->last_str, c, n);
    }

    /* Create a Str node out of last_str, if needed. It will be the
       last node in our expression list. */
    if (state->last_str) {
        expr_ty str = make_str_node_and_del(&state->last_str, c, n);
        if (!str || ExprList_Append(&state->expr_list, str) < 0)
            goto error;
    }
    /* This has already been freed. */
    assert(state->last_str == NULL);

    seq = ExprList_Finish(&state->expr_list, c->c_arena);
    if (!seq)
        goto error;

    /* If there's only one expression, return it. Otherwise, we need
       to join them together. */
    if (seq->size == 1)
        return seq->elements[0];

    return JoinedStr(seq, LINENO(n), n->n_col_offset, c->c_arena);

error:
    FstringParser_Dealloc(state);
    return NULL;
}

/* Given an f-string (with no 'f' or quotes) that's in str starting at
   ofs, parse it into an expr_ty. Return NULL on error. Does not
   decref str. */
static expr_ty
fstring_parse(PyObject *str, Py_ssize_t *ofs, int recurse_lvl,
              struct compiling *c, const node *n)
{
    FstringParser state;

    FstringParser_Init(&state);
    if (FstringParser_ConcatFstring(&state, str, ofs, recurse_lvl,
                                    c, n) < 0) {
        FstringParser_Dealloc(&state);
        return NULL;
    }

    return FstringParser_Finish(&state, c, n);
}

/* n is a Python string literal, including the bracketing quote
   characters, and r, b, u, &/or f prefixes (if any), and embedded
   escape sequences (if any). parsestr parses it, and returns the
   decoded Python string object.  If the string is an f-string, set
   *fmode and return the unparsed string object.
*/
static PyObject *
parsestr(struct compiling *c, const node *n, int *bytesmode, int *fmode)
{
    size_t len;
    const char *s = STR(n);
    int quote = Py_CHARMASK(*s);
    int rawmode = 0;
    int need_encoding;
    if (Py_ISALPHA(quote)) {
        while (!*bytesmode || !rawmode) {
            if (quote == 'b' || quote == 'B') {
                quote = *++s;
                *bytesmode = 1;
            }
            else if (quote == 'u' || quote == 'U') {
                quote = *++s;
            }
            else if (quote == 'r' || quote == 'R') {
                quote = *++s;
                rawmode = 1;
            }
            else if (quote == 'f' || quote == 'F') {
                quote = *++s;
                *fmode = 1;
            }
            else {
                break;
            }
        }
    }
    if (*fmode && *bytesmode) {
        PyErr_BadInternalCall();
        return NULL;
    }
    if (quote != '\'' && quote != '\"') {
        PyErr_BadInternalCall();
        return NULL;
    }
    /* Skip the leading quote char. */
    s++;
    len = strlen(s);
    if (len > INT_MAX) {
        PyErr_SetString(PyExc_OverflowError,
                        "string to parse is too long");
        return NULL;
    }
    if (s[--len] != quote) {
        /* Last quote char must match the first. */
        PyErr_BadInternalCall();
        return NULL;
    }
    if (len >= 4 && s[0] == quote && s[1] == quote) {
        /* A triple quoted string. We've already skipped one quote at
           the start and one at the end of the string. Now skip the
           two at the start. */
        s += 2;
        len -= 2;
        /* And check that the last two match. */
        if (s[--len] != quote || s[--len] != quote) {
            PyErr_BadInternalCall();
            return NULL;
        }
    }
    if (!*bytesmode && !rawmode) {
        return decode_unicode(c, s, len, c->c_encoding);
    }
    if (*bytesmode) {
        /* Disallow non-ascii characters (but not escapes) */
        const char *ch;
        for (ch = s; *ch; ch++) {
            if (Py_CHARMASK(*ch) >= 0x80) {
                ast_error(c, n, "bytes can only contain ASCII "
                          "literal characters.");
                return NULL;
            }
        }
    }
    need_encoding = (!*bytesmode && c->c_encoding != NULL &&
                     strcmp(c->c_encoding, "utf-8") != 0);
    if (rawmode || strchr(s, '\\') == NULL) {
        if (need_encoding) {
            PyObject *v, *u = PyUnicode_DecodeUTF8(s, len, NULL);
            if (u == NULL || !*bytesmode)
                return u;
            v = PyUnicode_AsEncodedString(u, c->c_encoding, NULL);
            Py_DECREF(u);
            return v;
        } else if (*bytesmode) {
            return PyBytes_FromStringAndSize(s, len);
        } else if (strcmp(c->c_encoding, "utf-8") == 0) {
            return PyUnicode_FromStringAndSize(s, len);
        } else {
            return PyUnicode_DecodeLatin1(s, len, NULL);
        }
    }
    return PyBytes_DecodeEscape(s, len, NULL, 1,
                                need_encoding ? c->c_encoding : NULL);
}

/* Accepts a STRING+ atom, and produces an expr_ty node. Run through
   each STRING atom, and process it as needed. For bytes, just
   concatenate them together, and the result will be a Bytes node. For
   normal strings and f-strings, concatenate them together. The result
   will be a Str node if there were no f-strings; a FormattedValue
   node if there's just an f-string (with no leading or trailing
   literals), or a JoinedStr node if there are multiple f-strings or
   any literals involved. */
static expr_ty
parsestrplus(struct compiling *c, const node *n)
{
    int bytesmode = 0;
    PyObject *bytes_str = NULL;
    int i;

    FstringParser state;
    FstringParser_Init(&state);

    for (i = 0; i < NCH(n); i++) {
        int this_bytesmode = 0;
        int this_fmode = 0;
        PyObject *s;

        REQ(CHILD(n, i), STRING);
        s = parsestr(c, CHILD(n, i), &this_bytesmode, &this_fmode);
        if (!s)
            goto error;

        /* Check that we're not mixing bytes with unicode. */
        if (i != 0 && bytesmode != this_bytesmode) {
            ast_error(c, n, "cannot mix bytes and nonbytes literals");
            Py_DECREF(s);
            goto error;
        }
        bytesmode = this_bytesmode;

        assert(bytesmode ? PyBytes_CheckExact(s) : PyUnicode_CheckExact(s));

        if (bytesmode) {
            /* For bytes, concat as we go. */
            if (i == 0) {
                /* First time, just remember this value. */
                bytes_str = s;
            } else {
                PyBytes_ConcatAndDel(&bytes_str, s);
                if (!bytes_str)
                    goto error;
            }
        } else if (this_fmode) {
            /* This is an f-string. Concatenate and decref it. */
            Py_ssize_t ofs = 0;
            int result = FstringParser_ConcatFstring(&state, s, &ofs, 0, c, n);
            Py_DECREF(s);
            if (result < 0)
                goto error;
        } else {
            /* This is a regular string. Concatenate it. */
            if (FstringParser_ConcatAndDel(&state, s) < 0)
                goto error;
        }
    }
    if (bytesmode) {
        /* Just return the bytes object and we're done. */
        if (PyArena_AddPyObject(c->c_arena, bytes_str) < 0)
            goto error;
        return Bytes(bytes_str, LINENO(n), n->n_col_offset, c->c_arena);
    }

    /* We're not a bytes string, bytes_str should never have been set. */
    assert(bytes_str == NULL);

    return FstringParser_Finish(&state, c, n);

error:
    Py_XDECREF(bytes_str);
    FstringParser_Dealloc(&state);
    return NULL;
}