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gh-130870: Preserve GenericAlias subclasses in typing.get_type_hints() #131583

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Merged
JelleZijlstra merged 3 commits into from
Jul 5, 2025
Merged

gh-130870: Preserve GenericAlias subclasses in typing.get_type_hints() #131583

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abd9aed
gh-130870: Preserve `GenericAlias` subclasses in `typing.get_type_hin…
Viicos Mar 22, 2025
137c916
Fix existing tests
Viicos Jun 10, 2025
d8408ea
Changelog
Viicos Jun 10, 2025
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gh-130870: Preserve GenericAlias subclasses in `typing.get_type_hin… 
…ts()`
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@Viicos
Viicos committed Jun 10, 2025
commit abd9aedd66124303155fcfb9566891f05b275848
18 changes: 18 additions & 0 deletions Lib/test/test_typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -7114,6 +7114,24 @@ def add_right(self, node: 'Node[T]' = None):
right_hints = get_type_hints(t.add_right, globals(), locals())
self.assertEqual(right_hints['node'], Node[T])

def test_get_type_hints_preserve_generic_alias_subclasses(self):
# https://github.com/python/cpython/issues/130870
# A real world example of this is `collections.abc.Callable`. When parameterized,
# the result is a subclass of `types.GenericAlias`.
class MyAlias(types.GenericAlias):
pass

class MyClass:
def __class_getitem__(cls, args):
return MyAlias(cls, args)

# Using a forward reference is important, otherwise it works as expected.
# `y` tests that the `GenericAlias` subclass is preserved when stripping `Annotated`.
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)


class GetUtilitiesTestCase(TestCase):
def test_get_origin(self):
Expand Down
26 changes: 16 additions & 10 deletions Lib/typing.py
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Expand Up @@ -407,6 +407,17 @@ def inner(*args, **kwds):
return decorator


def _rebuild_generic_alias(alias: GenericAlias, args: tuple[object, ...]) -> GenericAlias:
is_unpacked = alias.__unpacked__
if _should_unflatten_callable_args(alias, args):
t = alias.__origin__[(args[:-1], args[-1])]
else:
t = alias.__origin__[args]
if is_unpacked:
t = Unpack[t]
return t


def _deprecation_warning_for_no_type_params_passed(funcname: str) -> None:
import warnings

Expand Down Expand Up @@ -454,25 +465,20 @@ def _eval_type(t, globalns, localns, type_params=_sentinel, *, recursive_guard=f
_make_forward_ref(arg) if isinstance(arg, str) else arg
for arg in t.__args__
)
is_unpacked = t.__unpacked__
if _should_unflatten_callable_args(t, args):
t = t.__origin__[(args[:-1], args[-1])]
else:
t = t.__origin__[args]
if is_unpacked:
t = Unpack[t]
else:
args = t.__args__

ev_args = tuple(
_eval_type(
a, globalns, localns, type_params, recursive_guard=recursive_guard,
format=format, owner=owner,
)
for a in t.__args__
for a in args
)
if ev_args == t.__args__:
return t
if isinstance(t, GenericAlias):
return GenericAlias(t.__origin__, ev_args)
return _rebuild_generic_alias(t, ev_args)
if isinstance(t, Union):
return functools.reduce(operator.or_, ev_args)
else:
Expand Down Expand Up @@ -2404,7 +2410,7 @@ def _strip_annotations(t):
stripped_args = tuple(_strip_annotations(a) for a in t.__args__)
if stripped_args == t.__args__:
return t
return GenericAlias(t.__origin__, stripped_args)
return _rebuild_generic_alias(t, stripped_args)
if isinstance(t, Union):
stripped_args = tuple(_strip_annotations(a) for a in t.__args__)
if stripped_args == t.__args__:
Expand Down