Enum by-value lookup no longer compares hashable argument to unhashable values

[alien-valkyrie]

Bug report

Bug description:

When defining enum members with hashable values (e.g. frozensets), it was previously (prior to 3.13) possible to look those members up by passing in unhashable values (e.g. sets) that compare equal to those original values.
This no longer works as of 3.13 (specifically GH-112514), since the unhashable argument is now only compared to unhashable enum values. I haven't been able to find any documentation of this change in the What's New or even the changelog, so I'm assuming it's not entirely intended.

Reproducible example:

from enum import Enum

class Directions(Enum):
    DOWN_ONLY = frozenset({"sc"})
    UP_ONLY = frozenset({"cs"})
    UNRESTRICTED = frozenset({"sc", "cs"})

dirs = {"sc"}
# in 3.13, this raises ValueError
the_dirs = Directions(dirs)
assert the_dirs is Directions.DOWN_ONLY

Note that in this example (which is based on our use case) there's the obvious user-side fix of Directions(frozenset(dirs)), but if there happens to be another hashable-equal-to-unhashable use case outside of (frozen)sets, such a workaround might not exist.

CPython versions tested on:

3.13

Operating systems tested on:

Windows

Linked PRs

• gh-125710: [Enum] fix hashable<->nonhashable comparisons for member values #125735
• [3.13] gh-125710: [Enum] fix hashable<->nonhashable comparisons for member values (GH-125735) #125851