This is an old question, but none of the answers seems to mention that. in the general case, it IS possible for a new-style class to have different values for type(instance)
and instance.__class__
:
class ClassA(object):
def display(self):
print("ClassA")
class ClassB(object):
__class__ = ClassA
def display(self):
print("ClassB")
instance = ClassB()
print(type(instance))
print(instance.__class__)
instance.display()
Output:
<class '__main__.ClassB'>
<class '__main__.ClassA'>
ClassB
The reason is that ClassB
is overriding the __class__
descriptor, however the internal type field in the object is not changed. type(instance)
reads directly from that type field, so it returns the correct value, whereas instance.__class__
refers to the new descriptor replacing the original descriptor provided by Python, which reads the internal type field. Instead of reading that internal type field, it returns a hardcoded value.