Bug report

Bug description:

The memoryview builtin is registered as a Sequence, but doesn't implement the full API, because it doesn't inherit from Sequence at runtime and doesn't implement the mixin methods.

>>> import collections.abc
>>> issubclass(memoryview, collections.abc.Sequence)
True
>>> collections.abc.Sequence.index
<function Sequence.index at 0x10148d250>
>>> memoryview.index
Traceback (most recent call last):
  File "<python-input-4>", line 1, in <module>
    memoryview.index
AttributeError: type object 'memoryview' has no attribute 'index'

Among the methods listed for Sequence in the documentation, memoryview is missing __contains__, __reversed__, index, and count. This is causing problems for typing; in the typeshed stubs we have to either lie one way by claiming that memoryview has methods it doesn't have, or lie another way by claiming it is not a Sequence when issubclass() says otherwise at runtime (python/typeshed#12800). To fix this, we should either make memoryview not a Sequence, or add the missing methods. The former has compatibility implications, so I propose to add the methods in 3.14.

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-125420: implement Sequence.count API on memoryview objects #125443
• gh-125420: implement Sequence.index API on memoryview objects #125446
• (under consideration) gh-125420: implement Sequence.__contains__ API on memoryview objects #125441
• (under consideration) gh-125420: implement Sequence.__reversed__ API on memoryview objects #125505