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gh-133925: Make typing._UnionGenericAlias hashable #133929

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merged 2 commits into from
May 12, 2025
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gh-133925: Make typing._UnionGenericAlias hashable #133929

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gh-133925: Make typing._UnionGenericAlias hashable
JelleZijlstra May 12, 2025
2cb5476
hash should equal that of Union
JelleZijlstra May 12, 2025
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3 changes: 3 additions & 0 deletions Lib/test/test_typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -10668,6 +10668,9 @@ def test_eq(self):
with self.assertWarns(DeprecationWarning):
self.assertNotEqual(int, typing._UnionGenericAlias)

def test_hashable(self):
self.assertIsInstance(hash(typing._UnionGenericAlias), int)


def load_tests(loader, tests, pattern):
import doctest
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3 changes: 3 additions & 0 deletions Lib/typing.py
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Expand Up @@ -1649,6 +1649,9 @@ def __eq__(self, other):
return True
return NotImplemented

def __hash__(self):
return super().__hash__()
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This means that a Union instance and a _UnionGenericAlias instance might compare equal but hash differently, right? Might that do counterintuitive things if you used them as dictionary keys or put them in sets?

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I think that this is purely about the _UnionGenericAlias class itself, not _UnionGenericAlias instances.

Btw, do we need to add __hash__ tests to instances in other PR?

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I think that this is purely about the _UnionGenericAlias class itself, not _UnionGenericAlias instances.

ah, thanks, great point. It still seems like users are storing the classes themselves in sets, though, so I think my point still applies -- the bug report here comes from astropy/astropy#18126

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Yes, I should have made it hash() equal to Union. Fixed now.



class _UnionGenericAlias(metaclass=_UnionGenericAliasMeta):
"""Compatibility hack.
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2025-05-12-06-52-10.gh-issue-133925.elInBY.rst
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@@ -0,0 +1 @@
Make the private class ``typing._UnionGenericAlias`` hashable.
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