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[3.13] gh-139905: Provide suggestion in error message if Generic.__init_subclass__ was not called (GH-139943) (#139956)

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gh-139905: Provide suggestion in error message if `Generic.__init_subclass__` was not called (GH-139943)
(cherry picked from commit 5776d0d2e0)

Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>
This commit is contained in:
Miss Islington (bot) 2025-10-11 17:36:44 +02:00 • committed by GitHub
parent 6a9908ee94
commit cbb415e992
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3 changed files with 45 additions and 2 deletions
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16
Lib/typing.py
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@ -1236,14 +1236,26 @@ def _generic_class_getitem(cls, args):
f"Parameters to {cls.__name__}[...] must all be unique")
else:
# Subscripting a regular Generic subclass.
for param in cls.__parameters__:
try:
parameters = cls.__parameters__
except AttributeError as e:
init_subclass = getattr(cls, '__init_subclass__', None)
if init_subclass not in {None, Generic.__init_subclass__}:
e.add_note(
f"Note: this exception may have been caused by "
f"{init_subclass.__qualname__!r} (or the "
f"'__init_subclass__' method on a superclass) not "
f"calling 'super().__init_subclass__()'"
)
raise
for param in parameters:
prepare = getattr(param, '__typing_prepare_subst__', None)
if prepare is not None:
args = prepare(cls, args)
_check_generic_specialization(cls, args)
new_args = []
for param, new_arg in zip(cls.__parameters__, args):
for param, new_arg in zip(parameters, args):
if isinstance(param, TypeVarTuple):
new_args.extend(new_arg)
else: