How to compare two classes/types in python?

Question

I have two classes defined in a module classes.py:

class ClassA(object):
    pass

class ClassB(object):
    pass

And in another module I am getting the attributes of the module:

import classes

Class1 = getattr(classes, 'ClassA')
Class2 = getattr(classes, 'ClassA')
print type(Class1) == type(Class2)

Class3 = getattr(classes, 'ClassA')
Class4 = getattr(classes, 'ClassB')
print type(Class3) == type(Class4)

Both type comparison are returning True and that's not what I was expecting.

How can I compare class types using python's native type values?

Answer 1

If you want to check if types are equal then you should use is operator.

Example: we can create next stupid metaclass

class StupidMetaClass(type):
    def __eq__(self, other):
        return False

and then class based on it:

• in Python 2

    class StupidClass(object):
        __metaclass__ = StupidMetaClass
  

• in Python 3

  class StupidClass(metaclass=StupidMetaClass):
       pass
  
  

then a simple check

>>> StupidClass == StupidClass

returns False, while

>>> StupidClass is StupidClass

returns an expected True value.

So as we can see == operator on classes can be overloaded while there is no way (at least simple one) to change is operator's behavior.