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 "grammar.h"
#include "node.h"
#include "pyarena.h"
#include "ast.h"
#include "token.h"
#include "parsetok.h"
#include "graminit.h"

#include <assert.h>

/* Data structure used internally */
struct compiling {
    char *c_encoding; /* source encoding */
    PyArena *c_arena; /* arena for allocating memeory */
    const char *c_filename; /* filename */
};

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 *);

/* 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 PyObject *parsestr(struct compiling *, const node *n, int *bytesmode);
static PyObject *parsestrplus(struct compiling *, const node *n,
                              int *bytesmode);

#ifndef LINENO
#define LINENO(n)       ((n)->n_lineno)
#endif

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

static identifier
new_identifier(const char* n, PyArena *arena)
{
    PyObject* id = PyUnicode_DecodeUTF8(n, strlen(n), NULL);
    Py_UNICODE *u;
    if (!id)
        return NULL;
    u = PyUnicode_AS_UNICODE(id);
    /* Check whether there are non-ASCII characters in the
       identifier; if so, normalize to NFKC. */
    for (; *u; u++) {
        if (*u >= 128) {
            PyObject *m = PyImport_ImportModuleNoBlock("unicodedata");
            PyObject *id2;
            if (!m)
                return NULL;
            id2 = PyObject_CallMethod(m, "normalize", "sO", "NFKC", id);
            Py_DECREF(m);
            if (!id2)
                return NULL;
            Py_DECREF(id);
            id = id2;
            break;
        }
    }
    PyUnicode_InternInPlace(&id);
    PyArena_AddPyObject(arena, id);
    return id;
}

#define NEW_IDENTIFIER(n) new_identifier(STR(n), c->c_arena)

/* This routine provides an invalid object for the syntax error.
   The outermost routine must unpack this error and create the
   proper object.  We do this so that we don't have to pass
   the filename to everything function.

   XXX Maybe we should just pass the filename...
*/

static int
ast_error(const node *n, const char *errstr)
{
    PyObject *u = Py_BuildValue("zii", errstr, LINENO(n), n->n_col_offset);
    if (!u)
        return 0;
    PyErr_SetObject(PyExc_SyntaxError, u);
    Py_DECREF(u);
    return 0;
}

static void
ast_error_finish(const char *filename)
{
    PyObject *type, *value, *tback, *errstr, *offset, *loc, *tmp;
    PyObject *filename_obj;
    long lineno;

    assert(PyErr_Occurred());
    if (!PyErr_ExceptionMatches(PyExc_SyntaxError))
        return;

    PyErr_Fetch(&type, &value, &tback);
    errstr = PyTuple_GetItem(value, 0);
    if (!errstr)
        return;
    Py_INCREF(errstr);
    lineno = PyLong_AsLong(PyTuple_GetItem(value, 1));
    if (lineno == -1) {
        Py_DECREF(errstr);
        return;
    }
    offset = PyTuple_GetItem(value, 2);
    if (!offset) {
        Py_DECREF(errstr);
        return;
    }
    Py_DECREF(value);

    loc = PyErr_ProgramText(filename, lineno);
    if (!loc) {
        Py_INCREF(Py_None);
        loc = Py_None;
    }
    filename_obj = PyUnicode_DecodeFSDefault(filename);
    if (filename_obj != NULL)
        tmp = Py_BuildValue("(NlOO)", filename_obj, lineno, offset, loc);
    else
        tmp = NULL;
    Py_DECREF(loc);
    if (!tmp) {
        Py_DECREF(errstr);
        return;
    }
    value = PyTuple_Pack(2, errstr, tmp);
    Py_DECREF(errstr);
    Py_DECREF(tmp);
    if (!value)
        return;
    PyErr_Restore(type, value, tback);
}

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

    if (flags && flags->cf_flags & PyCF_SOURCE_IS_UTF8) {
        c.c_encoding = "utf-8";
        if (TYPE(n) == encoding_decl) {
#if 0
            ast_error(n, "encoding declaration in Unicode string");
            goto error;
#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";
    }
    c.c_arena = arena;
    c.c_filename = filename;

    k = 0;
    switch (TYPE(n)) {
        case file_input:
            stmts = asdl_seq_new(num_stmts(n), arena);
            if (!stmts)
                return NULL;
            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 error;
                    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 error;
                        asdl_seq_SET(stmts, k++, s);
                    }
                }
            }
            return Module(stmts, arena);
        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 error;
            return Expression(testlist_ast, arena);
        }
        case single_input:
            if (TYPE(CHILD(n, 0)) == NEWLINE) {
                stmts = asdl_seq_new(1, arena);
                if (!stmts)
                    goto error;
                asdl_seq_SET(stmts, 0, Pass(n->n_lineno, n->n_col_offset,
                                            arena));
                if (!asdl_seq_GET(stmts, 0))
                    goto error;
                return Interactive(stmts, arena);
            }
            else {
                n = CHILD(n, 0);
                num = num_stmts(n);
                stmts = asdl_seq_new(num, arena);
                if (!stmts)
                    goto error;
                if (num == 1) {
                    s = ast_for_stmt(&c, n);
                    if (!s)
                        goto error;
                    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 error;
                        asdl_seq_SET(stmts, i / 2, s);
                    }
                }

                return Interactive(stmts, arena);
            }
        default:
            PyErr_Format(PyExc_SystemError,
                         "invalid node %d for PyAST_FromNode", TYPE(n));
            goto error;
    }
 error:
    ast_error_finish(filename);
    return NULL;
}

/* 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 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(identifier name, const node *n, int full_checks)
{
    assert(PyUnicode_Check(name));
    if (PyUnicode_CompareWithASCIIString(name, "__debug__") == 0) {
        ast_error(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(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(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(e->v.Name.id, n, 1))
                    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:
            expr_name = "yield 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:
            expr_name = "literal";
            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(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;
        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 = 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
compiler_arg(struct compiling *c, const node *n)
{
    identifier name;
    expr_ty annotation = NULL;
    node *ch;

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

    return arg(name, annotation, c->c_arena);
#if 0
    result = Tuple(args, Store, LINENO(n), n->n_col_offset, c->c_arena);
    if (!set_context(c, result, Store, n))
        return NULL;
    return result;
#endif
}

/* 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(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(argname, ch, 0))
                    goto error;
                arg = arg(argname, annotation, c->c_arena);
                if (!arg)
                    goto error;
                asdl_seq_SET(kwonlyargs, j++, arg);
                i += 2; /* the name and the comma */
                break;
            case DOUBLESTAR:
                return i;
            default:
                ast_error(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] (',' tfpdef ['=' test])* [',' '**' tfpdef]
           | '**' tfpdef)
           | tfpdef ['=' test] (',' tfpdef ['=' test])* [','])
       tfpdef: NAME [':' test]
       varargslist: ((vfpdef ['=' test] ',')*
           ('*' [vfpdef] (',' vfpdef ['=' test])*  [',' '**' vfpdef]
           | '**' vfpdef)
           | vfpdef ['=' test] (',' vfpdef ['=' test])* [','])
       vfpdef: NAME
    */
    int i, j, k, nposargs = 0, nkwonlyargs = 0;
    int nposdefaults = 0, found_default = 0;
    asdl_seq *posargs, *posdefaults, *kwonlyargs, *kwdefaults;
    identifier vararg = NULL, kwarg = NULL;
    arg_ty arg;
    expr_ty varargannotation = NULL, kwargannotation = NULL;
    node *ch;

    if (TYPE(n) == parameters) {
        if (NCH(n) == 2) /* () as argument list */
            return arguments(NULL, NULL, 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 ? asdl_seq_new(nposargs, c->c_arena) : NULL);
    if (!posargs && nposargs)
        return NULL;
    kwonlyargs = (nkwonlyargs ?
                   asdl_seq_new(nkwonlyargs, c->c_arena) : NULL);
    if (!kwonlyargs && nkwonlyargs)
        return NULL;
    posdefaults = (nposdefaults ?
                    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 ?
                   asdl_seq_new(nkwonlyargs, c->c_arena) : NULL);
    if (!kwdefaults && nkwonlyargs)
        return NULL;

    if (nposargs + nkwonlyargs > 255) {
        ast_error(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(n,
                             "non-default argument follows default argument");
                    return NULL;
                }
                arg = compiler_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)) {
                    ast_error(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 = NEW_IDENTIFIER(CHILD(ch, 0));
                    if (!vararg)
                        return NULL;
                    if (forbidden_name(vararg, CHILD(ch, 0), 0))
                        return NULL;
                    if (NCH(ch) > 1) {
                        /* there is an annotation on the vararg */
                        varargannotation = ast_for_expr(c, CHILD(ch, 2));
                        if (!varargannotation)
                            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 = NEW_IDENTIFIER(CHILD(ch, 0));
                if (!kwarg)
                    return NULL;
                if (NCH(ch) > 1) {
                    /* there is an annotation on the kwarg */
                    kwargannotation = ast_for_expr(c, CHILD(ch, 2));
                    if (!kwargannotation)
                        return NULL;
                }
                if (forbidden_name(kwarg, CHILD(ch, 0), 0))
                    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, varargannotation, kwonlyargs, kwarg,
                    kwargannotation, posdefaults, kwdefaults, 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, 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 = 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(struct compiling *c, const node *n, asdl_seq *decorator_seq)
{
    /* 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(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;

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

static stmt_ty
ast_for_decorated(struct compiling *c, const node *n)
{
    /* decorated: decorators (classdef | 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)) == 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);
    }
    /* 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, 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 = 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 = 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 ( comp_for | (',' test)* [','] )
       argument: [test '='] test [comp_for]       # Really [keyword '='] test */
    expr_ty elt;
    asdl_seq *comps;

    assert(NCH(n) > 1);

    elt = ast_for_expr(c, CHILD(n, 0));
    if (!elt)
        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;
}

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

    assert(NCH(n) > 3);
    REQ(CHILD(n, 1), COLON);

    key = ast_for_expr(c, CHILD(n, 0));
    if (!key)
        return NULL;
    value = ast_for_expr(c, CHILD(n, 2));
    if (!value)
        return NULL;

    comps = ast_for_comprehension(c, CHILD(n, 3));
    if (!comps)
        return NULL;

    return DictComp(key, value, comps, 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_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);
    int bytesmode = 0;

    switch (TYPE(ch)) {
    case NAME: {
        /* All names start in Load context, but may later be
           changed. */
        PyObject *name = NEW_IDENTIFIER(ch);
        if (!name)
            return NULL;
        return Name(name, Load, LINENO(n), n->n_col_offset, c->c_arena);
    }
    case STRING: {
        PyObject *str = parsestrplus(c, n, &bytesmode);
        if (!str) {
            if (PyErr_ExceptionMatches(PyExc_UnicodeError)) {
                PyObject *type, *value, *tback, *errstr;
                PyErr_Fetch(&type, &value, &tback);
                errstr = PyObject_Str(value);
                if (errstr) {
                    char *s = "";
                    char buf[128];
                    s = _PyUnicode_AsString(errstr);
                    PyOS_snprintf(buf, sizeof(buf), "(unicode error) %s", s);
                    ast_error(n, buf);
                    Py_DECREF(errstr);
                } else {
                    ast_error(n, "(unicode error) unknown error");
                }
                Py_DECREF(type);
                Py_DECREF(value);
                Py_XDECREF(tback);
            }
            return NULL;
        }
        PyArena_AddPyObject(c->c_arena, str);
        if (bytesmode)
            return Bytes(str, LINENO(n), n->n_col_offset, c->c_arena);
        else
            return Str(str, LINENO(n), n->n_col_offset, c->c_arena);
    }
    case NUMBER: {
        PyObject *pynum = parsenumber(c, STR(ch));
        if (!pynum)
            return NULL;

        PyArena_AddPyObject(c->c_arena, pynum);
        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 ':' test)* [','] |
         *                 test (gen_for | (',' test)* [','])  */
        int i, size;
        asdl_seq *keys, *values;

        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 if (NCH(ch) == 1 || TYPE(CHILD(ch, 1)) == COMMA) {
            /* it's a simple set */
            asdl_seq *elts;
            size = (NCH(ch) + 1) / 2; /* +1 in case no trailing comma */
            elts = asdl_seq_new(size, c->c_arena);
            if (!elts)
                return NULL;
            for (i = 0; i < NCH(ch); i += 2) {
                expr_ty expression;
                expression = ast_for_expr(c, CHILD(ch, i));
                if (!expression)
                    return NULL;
                asdl_seq_SET(elts, i / 2, expression);
            }
            return Set(elts, LINENO(n), n->n_col_offset, c->c_arena);
        } else if (TYPE(CHILD(ch, 1)) == comp_for) {
            /* it's a set comprehension */
            return ast_for_setcomp(c, ch);
        } else if (NCH(ch) > 3 && TYPE(CHILD(ch, 3)) == comp_for) {
            return ast_for_dictcomp(c, ch);
        } else {
            /* it's a dict */
            size = (NCH(ch) + 1) / 4; /* +1 in case no trailing comma */
            keys = asdl_seq_new(size, c->c_arena);
            if (!keys)
                return NULL;

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

            for (i = 0; i < NCH(ch); i += 4) {
                expr_ty expression;

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

                asdl_seq_SET(keys, i / 4, expression);

                expression = ast_for_expr(c, CHILD(ch, i + 2));
                if (!expression)
                    return NULL;

                asdl_seq_SET(values, i / 4, expression);
            }
            return Dict(keys, values, LINENO(n), n->n_col_offset, c->c_arena);
        }
    }
    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, 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 = 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 = 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_power(struct compiling *c, const node *n)
{
    /* power: atom trailer* ('**' factor)*
     */
    int i;
    expr_ty e, tmp;
    REQ(n, power);
    e = ast_for_atom(c, CHILD(n, 0));
    if (!e)
        return NULL;
    if (NCH(n) == 1)
        return e;
    for (i = 1; i < NCH(n); 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 (TYPE(CHILD(n, NCH(n) - 1)) == factor) {
        expr_ty f = ast_for_expr(c, CHILD(n, NCH(n) - 1));
        if (!f)
            return NULL;
        tmp = BinOp(e, Pow, f, LINENO(n), n->n_col_offset, c->c_arena);
        if (!tmp)
            return NULL;
        e = tmp;
    }
    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 trailer* ('**' factor)*
    */

    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 = 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 = asdl_int_seq_new(NCH(n) / 2, c->c_arena);
                if (!ops)
                    return NULL;
                cmps = 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: {
            expr_ty exp = NULL;
            if (NCH(n) == 2) {
                exp = ast_for_testlist(c, CHILD(n, 1));
                if (!exp)
                    return NULL;
            }
            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 [',']| '*' test [',' '**' test]
               | '**' test)
      argument: [test '='] test [comp_for]        # Really [keyword '='] test
    */

    int i, nargs, nkeywords, ngens;
    asdl_seq *args;
    asdl_seq *keywords;
    expr_ty vararg = NULL, kwarg = NULL;

    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
                nkeywords++;
        }
    }
    if (ngens > 1 || (ngens && (nargs || nkeywords))) {
        ast_error(n, "Generator expression must be parenthesized "
                  "if not sole argument");
        return NULL;
    }

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

    args = asdl_seq_new(nargs + ngens, c->c_arena);
    if (!args)
        return NULL;
    keywords = asdl_seq_new(nkeywords, c->c_arena);
    if (!keywords)
        return NULL;
    nargs = 0;
    nkeywords = 0;
    for (i = 0; i < NCH(n); i++) {
        node *ch = CHILD(n, i);
        if (TYPE(ch) == argument) {
            expr_ty e;
            if (NCH(ch) == 1) {
                if (nkeywords) {
                    ast_error(CHILD(ch, 0),
                              "non-keyword arg after keyword arg");
                    return NULL;
                }
                if (vararg) {
                    ast_error(CHILD(ch, 0),
                              "only named arguments may follow *expression");
                    return NULL;
                }
                e = ast_for_expr(c, CHILD(ch, 0));
                if (!e)
                    return NULL;
                asdl_seq_SET(args, nargs++, e);
            }
            else if (TYPE(CHILD(ch, 1)) == comp_for) {
                e = ast_for_genexp(c, ch);
                if (!e)
                    return NULL;
                asdl_seq_SET(args, nargs++, e);
            }
            else {
                keyword_ty kw;
                identifier key, tmp;
                int k;

                /* CHILD(ch, 0) is test, but must be an identifier? */
                e = ast_for_expr(c, CHILD(ch, 0));
                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(CHILD(ch, 0), "lambda cannot contain assignment");
                  return NULL;
                } else if (e->kind != Name_kind) {
                  ast_error(CHILD(ch, 0), "keyword can't be an expression");
                  return NULL;
                } else if (forbidden_name(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 (!PyUnicode_Compare(tmp, key)) {
                        ast_error(CHILD(ch, 0), "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);
            }
        }
        else if (TYPE(ch) == STAR) {
            vararg = ast_for_expr(c, CHILD(n, i+1));
            if (!vararg)
                return NULL;
            i++;
        }
        else if (TYPE(ch) == DOUBLESTAR) {
            kwarg = ast_for_expr(c, CHILD(n, i+1));
            if (!kwarg)
                return NULL;
            i++;
        }
    }

    return Call(func, args, keywords, vararg, kwarg, 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(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 = 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(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 = 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
      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(str, str_node, 0))
                    return NULL;
            }
            else {
                if (forbidden_name(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(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(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);
                PyArena_AddPyObject(c->c_arena, str);
                return alias(str, NULL, c->c_arena);
            }
            break;
        case STAR:
            str = PyUnicode_InternFromString("*");
            PyArena_AddPyObject(c->c_arena, str);
            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 = 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(n, "trailing comma not allowed without"
                             " surrounding parentheses");
                return NULL;
            }
            break;
        default:
            ast_error(n, "Unexpected node-type in from-import");
            return NULL;
        }

        aliases = 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 = 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 = 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 = 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 = 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 = 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)
{
    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;

    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(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, *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(n, "malformed 'try' statement");
        return NULL;
    }

    if (n_except > 0) {
        int i;
        stmt_ty except_st;
        /* process except statements to create a try ... except */
        asdl_seq *handlers = 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);
        }

        except_st = TryExcept(body, handlers, orelse, LINENO(n),
                              n->n_col_offset, c->c_arena);
        if (!finally)
            return except_st;

        /* if a 'finally' is present too, we nest the TryExcept within a
           TryFinally to emulate try ... except ... finally */
        body = asdl_seq_new(1, c->c_arena);
        if (body == NULL)
            return NULL;
        asdl_seq_SET(body, 0, except_st);
    }

    /* must be a try ... finally (except clauses are in body, if any exist) */
    assert(finally != NULL);
    return TryFinally(body, finally, LINENO(n), n->n_col_offset, c->c_arena);
}

/* with_item: test ['as' expr] */
static stmt_ty
ast_for_with_item(struct compiling *c, const node *n, asdl_seq *content)
{
    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 With(context_expr, optional_vars, content, LINENO(n),
                n->n_col_offset, 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 i;
    stmt_ty ret;
    asdl_seq *inner;

    REQ(n, with_stmt);

    /* process the with items inside-out */
    i = NCH(n) - 1;
    /* the suite of the innermost with item is the suite of the with stmt */
    inner = ast_for_suite(c, CHILD(n, i));
    if (!inner)
        return NULL;

    for (;;) {
        i -= 2;
        ret = ast_for_with_item(c, CHILD(n, i), inner);
        if (!ret)
            return NULL;
        /* was this the last item? */
        if (i == 1)
            break;
        /* if not, wrap the result so far in a new sequence */
        inner = asdl_seq_new(1, c->c_arena);
        if (!inner)
            return NULL;
        asdl_seq_SET(inner, 0, ret);
    }

    return ret;
}

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(classname, CHILD(n, 3), 0))
            return NULL;
        return ClassDef(classname, NULL, NULL, 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(classname, CHILD(n, 3), 0))
            return NULL;
        return ClassDef(classname, NULL, NULL, 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(classname, CHILD(n, 1), 0))
        return NULL;

    return ClassDef(classname, call->v.Call.args, call->v.Call.keywords,
                    call->v.Call.starargs, call->v.Call.kwargs, 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
        */
        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);
            case try_stmt:
                return ast_for_try_stmt(c, ch);
            case with_stmt:
                return ast_for_with_stmt(c, ch);
            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);
            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((char *)s, (char **)&end, 0);
        if (x < 0 && errno == 0) {
            return PyLong_FromString((char *)s,
                                     (char **)0,
                                     0);
        }
    }
    else
        x = PyOS_strtol((char *)s, (char **)&end, 0);
    if (*end == '\0') {
        if (errno != 0)
            return PyLong_FromString((char *)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, char* encoding)
{
    PyObject *u, *v;
    char *s, *t;
    t = s = (char *)*sPtr;
    /* while (s < end && *s != '\\') s++; */ /* inefficient for u".." */
    while (s < end && (*s & 0x80)) s++;
    *sPtr = s;
    u = PyUnicode_DecodeUTF8(t, s - t, NULL);
    if (u == NULL)
        return NULL;
    v = PyUnicode_AsEncodedString(u, encoding, NULL);
    Py_DECREF(u);
    return v;
}

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

    if (encoding == NULL) {
        buf = (char *)s;
        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;
                char *r;
                Py_ssize_t rn, i;
                w = decode_utf8(c, &s, end, "utf-32-be");
                if (w == NULL) {
                    Py_DECREF(u);
                    return NULL;
                }
                r = PyBytes_AS_STRING(w);
                rn = Py_SIZE(w);
                assert(rn % 4 == 0);
                for (i = 0; i < rn; i += 4) {
                    sprintf(p, "\\U%02x%02x%02x%02x",
                            r[i + 0] & 0xFF,
                            r[i + 1] & 0xFF,
                            r[i + 2] & 0xFF,
                            r[i + 3] & 0xFF);
                    p += 10;
                }
                /* Should be impossible to overflow */
                assert(p - buf <= Py_SIZE(u));
                Py_DECREF(w);
            } else {
                *p++ = *s++;
            }
        }
        len = p - buf;
        s = buf;
    }
    if (rawmode)
        v = PyUnicode_DecodeRawUnicodeEscape(s, len, NULL);
    else
        v = PyUnicode_DecodeUnicodeEscape(s, len, NULL);
    Py_XDECREF(u);
    return v;
}

/* s is a Python string literal, including the bracketing quote characters,
 * and r &/or b prefixes (if any), and embedded escape sequences (if any).
 * parsestr parses it, and returns the decoded Python string object.
 */
static PyObject *
parsestr(struct compiling *c, const node *n, int *bytesmode)
{
    size_t len;
    const char *s = STR(n);
    int quote = Py_CHARMASK(*s);
    int rawmode = 0;
    int need_encoding;
    if (isalpha(quote)) {
        if (quote == 'b' || quote == 'B') {
            quote = *++s;
            *bytesmode = 1;
        }
        if (quote == 'r' || quote == 'R') {
            quote = *++s;
            rawmode = 1;
        }
    }
    if (quote != '\'' && quote != '\"') {
        PyErr_BadInternalCall();
        return NULL;
    }
    s++;
    len = strlen(s);
    if (len > INT_MAX) {
        PyErr_SetString(PyExc_OverflowError,
                        "string to parse is too long");
        return NULL;
    }
    if (s[--len] != quote) {
        PyErr_BadInternalCall();
        return NULL;
    }
    if (len >= 4 && s[0] == quote && s[1] == quote) {
        s += 2;
        len -= 2;
        if (s[--len] != quote || s[--len] != quote) {
            PyErr_BadInternalCall();
            return NULL;
        }
    }
    if (!*bytesmode && !rawmode) {
        return decode_unicode(c, s, len, rawmode, c->c_encoding);
    }
    if (*bytesmode) {
        /* Disallow non-ascii characters (but not escapes) */
        const char *c;
        for (c = s; *c; c++) {
            if (Py_CHARMASK(*c) >= 0x80) {
                ast_error(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);
}

/* Build a Python string object out of a STRING+ atom.  This takes care of
 * compile-time literal catenation, calling parsestr() on each piece, and
 * pasting the intermediate results together.
 */
static PyObject *
parsestrplus(struct compiling *c, const node *n, int *bytesmode)
{
    PyObject *v;
    int i;
    REQ(CHILD(n, 0), STRING);
    v = parsestr(c, CHILD(n, 0), bytesmode);
    if (v != NULL) {
        /* String literal concatenation */
        for (i = 1; i < NCH(n); i++) {
            PyObject *s;
            int subbm = 0;
            s = parsestr(c, CHILD(n, i), &subbm);
            if (s == NULL)
                goto onError;
            if (*bytesmode != subbm) {
                ast_error(n, "cannot mix bytes and nonbytes literals");
                goto onError;
            }
            if (PyBytes_Check(v) && PyBytes_Check(s)) {
                PyBytes_ConcatAndDel(&v, s);
                if (v == NULL)
                    goto onError;
            }
            else {
                PyObject *temp = PyUnicode_Concat(v, s);
                Py_DECREF(s);
                Py_DECREF(v);
                v = temp;
                if (v == NULL)
                    goto onError;
            }
        }
    }
    return v;

  onError:
    Py_XDECREF(v);
    return NULL;
}