8000 bpo-46998: Allow subclassing Any at runtime by hauntsaninja · Pull Request #31841 · python/cpython · GitHub
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bpo-46998: Allow subclassing Any at runtime #31841

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Merged
merged 15 commits into from
Apr 5, 2022
Merged

bpo-46998: Allow subclassing Any at runtime #31841

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bc71456
bpo-46998: Allow subclassing Any at runtime
Mar 13, 2022
abea39a
make error consistent
Mar 13, 2022
771f492
remove functools checks
Mar 13, 2022
900f2c7
📜🤖 Added by blurb_it.
blurb-it[bot] Mar 13, 2022
6e76441
more tests
Mar 13, 2022
b00ab17
Update Misc/NEWS.d/next/Library/2022-03-13-08-52-58.bpo-46998.cHh-9O.rst
hauntsaninja Mar 13, 2022
4d913ad
oops, fix test
Mar 13, 2022
1c1ab38
cooperative inheritance
Mar 13, 2022
4927e78
fix tests
Mar 13, 2022
68ea3a8
okay, make instancecheck work with multiple inheritance
Mar 13, 2022
f94b7e0
mention in docs
Mar 30, 2022
05db029
Merge remote-tracking branch 'upstream/main' into subclass-any
Mar 30, 2022
e11f405
fix pydoc test
Mar 30, 2022
63b00e4
add a sentence on reasoning
Mar 30, 2022
ac7b4a8
preposition
Mar 31, 2022
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make error consistent
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hauntsaninja committed Mar 13, 2022
commit abea39a381934b0d50a3be8048edf6367a3ff512
2 changes: 1 addition & 1 deletion Lib/typing.py
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Expand Up @@ -430,7 +430,7 @@ def __getitem__(self, parameters):

class _AnyMeta(type):
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The metaclass is unfortunate because it restricts what classes can double-inherit from Any (due to metaclass conflicts). Seems unavoidable though.

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@hauntsaninja hauntsaninja Mar 13, 2022 •
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Not entirely unavoidable, if we were willing to give up on instancecheck (and repr), I'd say we could just remove the metaclass entirely

def __instancecheck__(self, obj):
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Should we even have this? isinstance(X, Any) is now a meaningful operation.

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@hauntsaninja hauntsaninja Mar 13, 2022 •
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I'm fine with removing it (as this PR currently does for issubclass). Doing so would also allow us to get rid of the metaclass, which will help remove restrictions on what classes can inherit from Any.

My reasoning for keeping it is that isinstance is very commonly used, potentially by typing / Python novices, and isinstance(..., Any) doesn't correspond well to the notion of Any at type check time. Sophisticated users have workarounds available to them for the equivalent isinstance check.

raise TypeError("Any cannot be used with isinstance()")
raise TypeError("typing.Any cannot be used with isinstance()")

def __repr__(self):
return "typing.Any"
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