Ensure we only weakref() obj once#5
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eendebakpt merged 3 commits intoeendebakpt:singledispatchmethod3from Jul 31, 2023
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eendebakpt
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Lib/functools.py
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| def __get__(self, obj, cls=None): | ||
| if self._all_weakrefable_instances and cls is not None and obj in self._method_cache: | ||
| return self._method_cache[obj] | ||
| caching = self._all_weakrefable_instances and obj is not None |
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This does no longer check for cls is not None. Is that ok? I could not construct any test cases where cls = None, so in my PR i kept it in.
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I think it's okay. The tests I added in this PR fail if we don't do the if obj is not None check. But, like you, I couldn't come up with a test case where cls=None. I'm also not actually sure why it would be a problem if cls=None for our caching here.
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https://docs.python.org/3/howto/descriptor.html#overview-of-descriptor-invocation appears to confirm that desc.__get__(obj, None) is semantically equivalent to desc.__get__(obj, type(obj))
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The performance characteristics of
WeakKeyDictionary()seem pretty different todict, so going back to atry/except KeyErrorstructure actually seems much more performant now we're using aWeakKeyDictionaryfor the non-slotted case, and doesn't seem to cost us anything for the slotted case