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gh-137226: Fix get_type_hints() on generic TypedDict with stringified annotations by JelleZijlstra · Pull Request #138953 · python/cpython · GitHub

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gh-137226: Fix get_type_hints() on generic TypedDict with stringified annotations #138953

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Merged
JelleZijlstra merged 2 commits into from
Sep 16, 2025
+39 −12
Conversation 8 Commits 2 Checks 51 Files changed 3
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gh-137226: Fix get_type_hints() on generic TypedDict with stringified annotations #138953

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gh-137226: Fix get_type_hints() on generic TypedDict with stringified…
JelleZijlstra Sep 15, 2025
58f97cd
remove still-broken test
JelleZijlstra Sep 15, 2025
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17 changes: 15 additions & 2 deletions Lib/test/test_typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -7172,6 +7172,19 @@ def func(x: MyClass['int'], y: MyClass[Annotated[int, ...]]): ...
assert isinstance(get_type_hints(func)['x'], MyAlias)
assert isinstance(get_type_hints(func)['y'], MyAlias)

def test_stringified_typeddict(self):
ns = run_code(
"""
from __future__ import annotations
from typing import TypedDict
class TD[UniqueT](TypedDict):
a: UniqueT
"""
)
TD = ns['TD']
self.assertEqual(TD.__annotations__, {'a': EqualToForwardRef('UniqueT', owner=TD, module=TD.__module__)})
self.assertEqual(get_type_hints(TD), {'a': TD.__type_params__[0]})


class GetUtilitiesTestCase(TestCase):
def test_get_origin(self):
Expand Down Expand Up @@ -8657,8 +8670,8 @@ def _make_td(future, class_name, annos, base, extra_names=None):
child = _make_td(
child_future, "Child", {"child": "int"}, "Base", {"Base": base}
)
base_anno = ForwardRef("int", module="builtins") if base_future else int
child_anno = ForwardRef("int", module="builtins") if child_future else int
base_anno = ForwardRef("int", module="builtins", owner=base) if base_future else int
child_anno = ForwardRef("int", module="builtins", owner=child) if child_future else int
self.assertEqual(base.__annotations__, {'base': base_anno})
self.assertEqual(
child.__annotations__, {'child': child_anno, 'base': base_anno}
Expand Down
32 changes: 22 additions & 10 deletions Lib/typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -171,16 +171,16 @@ def __getattr__(self, attr):
_lazy_annotationlib = _LazyAnnotationLib()


def _type_convert(arg, module=None, *, allow_special_forms=False):
def _type_convert(arg, module=None, *, allow_special_forms=False, owner=None):
"""For converting None to type(None), and strings to ForwardRef."""
if arg is None:
return type(None)
if isinstance(arg, str):
return _make_forward_ref(arg, module=module, is_class=allow_special_forms)
return _make_forward_ref(arg, module=module, is_class=allow_special_forms, owner=owner)
return arg


def _type_check(arg, msg, is_argument=True, module=None, *, allow_special_forms=False):
def _type_check(arg, msg, is_argument=True, module=None, *, allow_special_forms=False, owner=None):
"""Check that the argument is a type, and return it (internal helper).

As a special case, accept None and return type(None) instead. Also wrap strings
Expand All @@ -198,7 +198,7 @@ def _type_check(arg, msg, is_argument=True, module=None, *, allow_special_forms=
if is_argument:
invalid_generic_forms += (Final,)

arg = _type_convert(arg, module=module, allow_special_forms=allow_special_forms)
arg = _type_convert(arg, module=module, allow_special_forms=allow_special_forms, owner=owner)
if (isinstance(arg, _GenericAlias) and
arg.__origin__ in invalid_generic_forms):
raise TypeError(f"{arg} is not valid as type argument")
Expand Down Expand Up @@ -454,7 +454,7 @@ def _deprecation_warning_for_no_type_params_passed(funcname: str) -> None:


def _eval_type(t, globalns, localns, type_params, *, recursive_guard=frozenset(),
format=None, owner=None, parent_fwdref=None):
format=None, owner=None, parent_fwdref=None, prefer_fwd_module=False):

AlexWaygood Sep 16, 2025 •
edited
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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Could we add a description of this parameter to the docstring?

Should this default to True? Third-party users of this function may be expecting the legacy get_type_hints behaviour? They're obviously asking for breakage if they're using an undocumented, private implementation detail though. So I don't have a strong opinion here.

JelleZijlstra Sep 16, 2025

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

I think the False behavior is more sensible so I want to default to it. I know this function gets used in the wild and we shouldn't go out of our way to break such uses, but at the end of the day it's a private function.
"""Evaluate all forward references in the given type t.

For use of globalns and localns see the docstring for get_type_hints().
Expand All @@ -464,8 +464,20 @@ def _eval_type(t, globalns, localns, type_params, *, recursive_guard=frozenset()
if isinstance(t, _lazy_annotationlib.ForwardRef):
# If the forward_ref has __forward_module__ set, evaluate() infers the globals
# from the module, and it will probably pick better than the globals we have here.
if t.__forward_module__ is not None:
# We do this only for calls from get_type_hints() (which opts in through the
# prefer_fwd_module flag), so that the default behavior remains more straightforward.
if prefer_fwd_module and t.__forward_module__ is not None:
globalns = None
# If there are type params on the owner, we need to add them back, because
# annotationlib won't.
if owner_type_params := getattr(owner, "__type_params__", None):
globalns = getattr(
sys.modules.get(t.__forward_module__, None), "__dict__", None
)
if globalns is not None:
globalns = dict(globalns)
for type_param in owner_type_params:
globalns[type_param.__name__] = type_param
return evaluate_forward_ref(t, globals=globalns, locals=localns,
type_params=type_params, owner=owner,
_recursive_guard=recursive_guard, format=format)
Expand All @@ -481,7 +493,7 @@ def _eval_type(t, globalns, localns, type_params, *, recursive_guard=frozenset()
ev_args = tuple(
_eval_type(
a, globalns, localns, type_params, recursive_guard=recursive_guard,
format=format, owner=owner,
format=format, owner=owner, prefer_fwd_module=prefer_fwd_module,
)
for a in args
)
Expand Down Expand Up @@ -2369,7 +2381,7 @@ def get_type_hints(obj, globalns=None, localns=None, include_extras=False,
if isinstance(value, str):
value = _make_forward_ref(value, is_argument=False, is_class=True)
value = _eval_type(value, base_globals, base_locals, (),
format=format, owner=obj)
format=format, owner=obj, prefer_fwd_module=True)
if value is None:
value = type(None)
hints[name] = value
Expand Down Expand Up @@ -2414,7 +2426,7 @@ def get_type_hints(obj, globalns=None, localns=None, include_extras=False,
is_argument=not isinstance(obj, types.ModuleType),
is_class=False,
)
value = _eval_type(value, globalns, localns, (), format=format, owner=obj)
value = _eval_type(value, globalns, localns, (), format=format, owner=obj, prefer_fwd_module=True)
if value is None:
value = type(None)
hints[name] = value
Expand Down Expand Up @@ -3111,7 +3123,7 @@ def __new__(cls, name, bases, ns, total=True):
own_annotations = {}
msg = "TypedDict('Name', {f0: t0, f1: t1, ...}); each t must be a type"
own_checked_annotations = {
n: _type_check(tp, msg, module=tp_dict.__module__)
n: _type_check(tp, msg, owner=tp_dict, module=tp_dict.__module__)
for n, tp in own_annotations.items()
}
required_keys = set()
Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2025-09-15-13-09-19.gh-issue-137226.HH3_ik.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix :func:`typing.get_type_hints` calls on generic :class:`typing.TypedDict`
classes defined with string annotations.
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