pathological python

gistfile1.txt

mwhudson@aeglos:~$ cat mro.py 
class T(type):
    def mro(self):
        return []

class X(object,metaclass=T):
    pass

class Y(object):
    pass

x = Y()
x.__class__ = X
print(isinstance(x, object))
mwhudson@aeglos:~$ python3 mro.py 
False

On Python 3.6.x:

Traceback (most recent call last):
  File "pathological.py", line 5, in <module>
    class X(object,metaclass=T):
TypeError: super(type, obj): obj must be an instance or subtype of type