[3.10] bpo-44524: Fix cryptic TypeError message when trying to subclass special forms in typing (GH-27710)
#27815
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…ial forms in `typing` (pythonGH-27710) This was a Python 3.9 regression. (cherry picked from commit a3a4d20) Co-authored-by: Yurii Karabas <[email protected]>
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@pablogsal, this is only a TypeError message improvement. Before: >>> class C(Union[int, str]): ...
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its basesAfter: >>> class C(Union[int, str]): ...
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: Cannot subclass <class 'typing._SpecialForm'>The "after" was the situation before Python 3.9.0. |
pablogsal
approved these changes
Aug 28, 2021
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This was a Python 3.9 regression.
(cherry picked from commit a3a4d20)
Co-authored-by: Yurii Karabas [email protected]
https://bugs.python.org/issue44524
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