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bpo-46642: explicitly disallow typing.TypeVar instance subclassing #31148

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Jun 25, 2022
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bpo-46642: explicitly disallow typing.TypeVar instance subclassing #31148

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c51f48e
explicitly disallow typing.TypeVar subclassing
GBeauregard Feb 5, 2022
3659772
📜🤖 Added by blurb_it.
blurb-it[bot] Feb 5, 2022
a3c54d5
make test match regex
GBeauregard Feb 6, 2022
3b68cda
Merge branch 'python:main' into fix-typevar-test
GBeauregard Feb 6, 2022
a7a6074
Merge branch 'main' into fix-typevar-test
serhiy-storchaka Jun 21, 2022
bf233d1
More explicit errors and more tests.
serhiy-storchaka Jun 21, 2022
a854d32
Update a NEWS entry.
serhiy-storchaka Jun 21, 2022
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3 changes: 3 additions & 0 deletions Lib/typing.py
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Expand Up @@ -818,6 +818,9 @@ def __init__(self, name, *constraints, bound=None,
if def_mod != 'typing':
self.__module__ = def_mod

def __mro_entries__(self, bases):
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It should be added not here, but in _TypeVarLike. ParamSpec instances are not subclassable too.

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And add it also in TypeVarTuple.

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Thanks for the feedback! I'll get to this soon and ping you when done (I'm currently in the process of moving across the country and starting a job)

raise TypeError("Cannot subclass an instance of TypeVar.")


class ParamSpecArgs(_Final, _Immutable, _root=True):
"""The args for a ParamSpec object.
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2022-02-05-18-46-54.bpo-46642.YI6nHQ.rst
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@@ -0,0 +1 @@
Improve error message when trying to subclass an instance of :data:`typing.TypeVar`. Patch by Gregory Beauregard.