We'll use the BlackJackCard class as an example to see what happens when we attempt comparisons where the two operands are from different classes.

The following is a Card instance that we can compare against the int values:

>>> two = card21(2, "♠")
>>> two < 2 
Traceback (most recent call last): 
  File "<stdin>", line 1, in <module> 
TypeError: unorderable types: Number21Card() < int() 
>>> two > 2 
Traceback (most recent call last): 
  File "<stdin>", line 1, in <module> 
TypeError: unorderable types: Number21Card() > int() 

This is what we expected: the subclass of BlackJackCard, Number21Card, doesn't provide the required special methods to implement a comparison against integers, so there's a TypeError exception. However, consider the following two examples:

>>> two == 2
False
>>> 2 == two
False

Why do these provide responses? When confronted with a NotImplemented value, Python will reverse the operands. In this case, the integer value, 2, defines the int.__eq__() method, which tolerates objects of an unexpected class.