Side-effect of ABC.__subclasshook__ / _abc_instancecheck ▶ isinstance(..., Parent) calls __subclasscheck__ of uninvolved Child class -> RecursionError #136713
Description
Bug report
Bug description:
I realized there is strange error of __subclasshook__, or possibly _abc_instancecheck which creates a side-effect that __subclasshook__ is called on a Child class that is not even queried.
What is even more strange this error only occurs when the crucial statement B is called in a AB situation, just B or BAB is fine.
# At the end of his snippet are 3 test sets, Only the first causes an error the other 2 are fine.
import sys
sys.setrecursionlimit(59)
from abc import ABC
class Base(ABC): ...
class _ParentCheck(Base):
@classmethod
def __subclasshook__(cls, subclass):
if not issubclass(subclass, Base):
return NotImplemented
if not hasattr(subclass, "f"):
return False
return True
class Parent(Base):
f: int
@classmethod
def construct(cls, foo: int):
class Child(cls, _ParentCheck):
f = foo
return Child
# Test Set 1: Error
assert issubclass(Parent.construct(1), Parent) # Statement A
assert not isinstance(lambda: None, Parent) # Statement B
# Test Set 2: OK
assert not isinstance(lambda: None, Parent) # Statement B
# Test Set 3: OK
assert not isinstance(lambda: None, Parent) # Statement B
assert issubclass(Parent.construct(1), Parent) # Statement A
assert not isinstance(lambda: None, Parent) # Statement BCPython versions tested on:
3.14
Operating systems tested on:
Linux