Skip to content

[3.9] bpo-42195: Override _CallableGenericAlias's __getitem__ (GH-23915) #23916

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Dec 24, 2020
Merged

[3.9] bpo-42195: Override _CallableGenericAlias's __getitem__ (GH-23915) #23916

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
12 changes: 11 additions & 1 deletion Lib/_collections_abc.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -441,7 +441,7 @@ def __create_ga(cls, origin, args):
raise TypeError(
"Callable must be used as Callable[[arg, ...], result].")
t_args, t_result = args
if isinstance(t_args, list):
if isinstance(t_args, (list, tuple)):
ga_args = tuple(t_args) + (t_result,)
# This relaxes what t_args can be on purpose to allow things like
# PEP 612 ParamSpec. Responsibility for whether a user is using
Expand All @@ -463,6 +463,16 @@ def __reduce__(self):
args = list(args[:-1]), args[-1]
return _CallableGenericAlias, (Callable, args)

def __getitem__(self, item):
# Called during TypeVar substitution, returns the custom subclass
# rather than the default types.GenericAlias object.
ga = super().__getitem__(item)
args = ga.__args__
t_result = args[-1]
t_args = args[:-1]
args = (t_args, t_result)
return _CallableGenericAlias(Callable, args)


def _type_repr(obj):
"""Return the repr() of an object, special-casing types (internal helper).
Expand Down
6 changes: 6 additions & 0 deletions Lib/test/test_genericalias.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -347,6 +347,12 @@ def test_abc_callable(self):
self.assertEqual(C2[int, float, str], Callable[[int, float], str])
self.assertEqual(C3[int], Callable[..., int])

# multi chaining
C4 = C2[int, V, str]
self.assertEqual(repr(C4).split(".")[-1], "Callable[[int, ~V], str]")
self.assertEqual(repr(C4[dict]).split(".")[-1], "Callable[[int, dict], str]")
self.assertEqual(C4[dict], Callable[[int, dict], str])

with self.subTest("Testing type erasure"):
class C1(Callable):
def __call__(self):
Expand Down