New submission from Terry J. Reedy <tjre...@udel.edu>:
Consider class Object defined as follows:
import types
class Type(type):
__class__ = property({}.__getitem__, {}.__setitem__)
class Object(metaclass=Type):
__slots__ = '__class__'
isinstance(Object, ob) is true for type and Type and false for anything else.
But for the examples of the latter that I tried, (list, int, types.CodeType,
types.MethodType, see attached tem3.py), it incorrectly raises
KeyError: <class '__main__.Object'>
I cannot find the C source for isinstance. In Python/bltinmodule.c, function
builtin_isinstance_impl wraps
retval = PyObject_IsInstance(obj, class_or_tuple);
but grepping for PyObject_IsInstance in *.c and *.h only returned other calls.
----------
components: Interpreter Core
files: tem3.py
messages: 365774
nosy: terry.reedy
priority: normal
severity: normal
stage: needs patch
status: open
title: isinstance(cls_with_metaclass, non_type) raises KeyError
type: behavior
versions: Python 3.7, Python 3.8, Python 3.9
Added file: https://bugs.python.org/file49034/tem3.py
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<https://bugs.python.org/issue40180>
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