Question

Why does this happen?

class IsInstanceScrewer(object):
    def __init__(self, value):
        self.value = value

    def __getattribute__(self, name):
        if name in ('value',):
            return object.__getattribute__(self, name)
        value = object.__getattribute__(self, 'value')
        return object.__getattribute__(value, name)

isinstance(IsInstanceScrewer(False), bool) #True
isinstance(IsInstanceScrewer([1, 2, 3]), list) #True

The class is definitely not an instance of bool, even though it attempts to wrap it.

Answer 1

__getattribute__ is returning the __class__ of the wrapped value instead of its own __class__:

>>> class IsInstanceScrewer(object):
    def __init__(self, value):
        self.value = value

    def __getattribute__(self, name):
        print name
        if name in ('value',):
            return object.__getattribute__(self, name)
        value = object.__getattribute__(self, 'value')
        return object.__getattribute__(value, name)

>>> isinstance(IsInstanceScrewer(False), bool)
__class__
True
>>> isinstance(IsInstanceScrewer([1, 2, 3]), list)
__class__
True

This may be desired behavior or not depending on what you’re doing.