Description

uwu-crj

opened on Sep 20, 2026

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Bug report

Bug description:

Compare these two timeit invocations:

$ python3.14 -m timeit -s 'class Test: pass' -s 't = Test()' 'hasattr(t,"x")'
10000000 loops, best of 5: 33.5 nsec per loop
$ python3.14 -m timeit -s 'class Test: __slots__ = ("x",)' -s 't = Test()' 'hasattr(t,"x")'
1000000 loops, best of 5: 241 nsec per loop

Observe that in the case where Test.x is a slot, hasattr takes 241 ns to return False while it only takes 33.5 ns when there is no Test.x slot.

Peter Bierma advised me to file an issue when I asked about this in Discourse.

CPython versions tested on:

3.14, 3.13, 3.12

Operating systems tested on:

Linux

Linked PRs

• gh-157840: Special-case member descriptors when using hasattr #157866

Activity

1. uwu-crj

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Sep 20, 2026
2. aisk

   added

   type-featureA feature request or enhancementA feature request or enhancement

   performancePerformance or resource usagePerformance or resource usage

   interpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)

   and removed

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Sep 20, 2026
3. ZeroIntensity

   self-assigned this

   on Sep 20, 2026
4. ZeroIntensity

   added a commit that references this issue on Sep 20, 2026

   gh-157840: Special-case member descriptors when using `hasattr` (GH-1…

   41d0922
5. ZeroIntensity

   closed this as completedon Sep 20, 2026

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