isinstance(obj, Hashable) raises TypeError when both obj and type(obj) are unhashable #129589
Description
Bug report
Bug description:
Assumption: isinstance(anything, any_type) should never raise.
The problem appears to be in _abc.c function _abc__abc_subclasscheck_impl (known at runtime as _abc._abc_subclasscheck()), which reads (in part):
/* 1. Check cache. */
incache = _in_weak_set(impl->_abc_cache, subclass);
The implementation assumes subclass is hashable. That's almost always true of classes, but not guaranteed.
Reproduction case:
from __future__ import annotations
from collections.abc import Hashable
class UnhashableMeta(type):
def __eq__(self, other: object) -> bool:
return super().__eq__(other)
class UnhashableClass(metaclass=UnhashableMeta):
def __eq__(self, other: object) -> bool:
return super().__eq__(other)
# any non-hashable instance of a non-hashable class
# ┌────────┴────────┐
isinstance(UnhashableClass(), Hashable)Traceback for (cpython) Python 3.13.1:
Traceback (most recent call last):
File "<frozen runpy>", line 198, in _run_module_as_main
File "<frozen runpy>", line 88, in _run_code
File ".../bug.py", line 14, in <module>
isinstance(UnhashableClass(), Hashable)
~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "<frozen abc>", line 119, in __instancecheck__
File "<frozen abc>", line 123, in __subclasscheck__
TypeError: unhashable type: 'UnhashableMeta'
Tracebacks are nearly identical with Python 3.8, 3.9, 3.10, 3.11, and 3.12, as well as Python 3.14.0a4.
CPython versions tested on:
3.13, 3.12, 3.11, 3.10, 3.9, 3.14
Operating systems tested on:
macOS