bpo-38605: Make 'from __future__ import annotations' the default (GH-20434)
The hard part was making all the tests pass; there are some subtle issues here, because apparently the future import wasn't tested very thoroughly in previous Python versions.
For example, `inspect.signature()` returned type objects normally (except for forward references), but strings with the future import. We changed it to try and return type objects by calling `typing.get_type_hints()`, but fall back on returning strings if that function fails (which it may do if there are future references in the annotations that require passing in a specific namespace to resolve).
diff --git a/Python/ast_opt.c b/Python/ast_opt.c
index 5efaac4..22ca6f2 100644
--- a/Python/ast_opt.c
+++ b/Python/ast_opt.c
@@ -392,7 +392,6 @@
static int astfold_arguments(arguments_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
static int astfold_comprehension(comprehension_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
static int astfold_keyword(keyword_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
-static int astfold_arg(arg_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
static int astfold_withitem(withitem_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
static int astfold_excepthandler(excepthandler_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
#define CALL(FUNC, TYPE, ARG) \
@@ -595,26 +594,12 @@
static int
astfold_arguments(arguments_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
{
- CALL_SEQ(astfold_arg, arg, node_->posonlyargs);
- CALL_SEQ(astfold_arg, arg, node_->args);
- CALL_OPT(astfold_arg, arg_ty, node_->vararg);
- CALL_SEQ(astfold_arg, arg, node_->kwonlyargs);
CALL_SEQ(astfold_expr, expr, node_->kw_defaults);
- CALL_OPT(astfold_arg, arg_ty, node_->kwarg);
CALL_SEQ(astfold_expr, expr, node_->defaults);
return 1;
}
static int
-astfold_arg(arg_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
-{
- if (!(state->ff_features & CO_FUTURE_ANNOTATIONS)) {
- CALL_OPT(astfold_expr, expr_ty, node_->annotation);
- }
- return 1;
-}
-
-static int
astfold_stmt(stmt_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
{
switch (node_->kind) {
@@ -622,17 +607,11 @@
CALL(astfold_arguments, arguments_ty, node_->v.FunctionDef.args);
CALL(astfold_body, asdl_seq, node_->v.FunctionDef.body);
CALL_SEQ(astfold_expr, expr, node_->v.FunctionDef.decorator_list);
- if (!(state->ff_features & CO_FUTURE_ANNOTATIONS)) {
- CALL_OPT(astfold_expr, expr_ty, node_->v.FunctionDef.returns);
- }
break;
case AsyncFunctionDef_kind:
CALL(astfold_arguments, arguments_ty, node_->v.AsyncFunctionDef.args);
CALL(astfold_body, asdl_seq, node_->v.AsyncFunctionDef.body);
CALL_SEQ(astfold_expr, expr, node_->v.AsyncFunctionDef.decorator_list);
- if (!(state->ff_features & CO_FUTURE_ANNOTATIONS)) {
- CALL_OPT(astfold_expr, expr_ty, node_->v.AsyncFunctionDef.returns);
- }
break;
case ClassDef_kind:
CALL_SEQ(astfold_expr, expr, node_->v.ClassDef.bases);
@@ -656,9 +635,6 @@
break;
case AnnAssign_kind:
CALL(astfold_expr, expr_ty, node_->v.AnnAssign.target);
- if (!(state->ff_features & CO_FUTURE_ANNOTATIONS)) {
- CALL(astfold_expr, expr_ty, node_->v.AnnAssign.annotation);
- }
CALL_OPT(astfold_expr, expr_ty, node_->v.AnnAssign.value);
break;
case For_kind:
diff --git a/Python/compile.c b/Python/compile.c
index f2563d7..ddd2a04 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -2026,12 +2026,7 @@
{
if (annotation) {
PyObject *mangled;
- if (c->c_future->ff_features & CO_FUTURE_ANNOTATIONS) {
- VISIT(c, annexpr, annotation)
- }
- else {
- VISIT(c, expr, annotation);
- }
+ VISIT(c, annexpr, annotation);
mangled = _Py_Mangle(c->u->u_private, id);
if (!mangled)
return 0;
@@ -5261,12 +5256,7 @@
if (s->v.AnnAssign.simple &&
(c->u->u_scope_type == COMPILER_SCOPE_MODULE ||
c->u->u_scope_type == COMPILER_SCOPE_CLASS)) {
- if (c->c_future->ff_features & CO_FUTURE_ANNOTATIONS) {
- VISIT(c, annexpr, s->v.AnnAssign.annotation)
- }
- else {
- VISIT(c, expr, s->v.AnnAssign.annotation);
- }
+ VISIT(c, annexpr, s->v.AnnAssign.annotation);
ADDOP_NAME(c, LOAD_NAME, __annotations__, names);
mangled = _Py_Mangle(c->u->u_private, targ->v.Name.id);
ADDOP_LOAD_CONST_NEW(c, mangled);
diff --git a/Python/future.c b/Python/future.c
index 3cea4fe..4b73eb6 100644
--- a/Python/future.c
+++ b/Python/future.c
@@ -41,7 +41,7 @@
} else if (strcmp(feature, FUTURE_GENERATOR_STOP) == 0) {
continue;
} else if (strcmp(feature, FUTURE_ANNOTATIONS) == 0) {
- ff->ff_features |= CO_FUTURE_ANNOTATIONS;
+ continue;
} else if (strcmp(feature, "braces") == 0) {
PyErr_SetString(PyExc_SyntaxError,
"not a chance");