When looking at a blackjack Hand object, we have an interesting special case for containment. We often want to know if there's an ace in the hand. If we define Hand as an extension to list, then we can't ask for a generic ace. We can only ask for specific cards. We hate to write something like this:

any( card(1,suit) for suit in Suits )

That seems a long-winded way to look for an ace in a hand.

Here's a better example, but it still is less-than-ideal, perhaps:

any( c.rank == 'A' for c in hand.cards )

So, we'd like something like this:

'A' in hand.cards

This means that we're modifying the meaning of "contains" for a Hand object that extends list. We're not looking for a Card instance, we're merely looking for the rank property of a Card object. We can override the __contains__() method to do this:

def __contains__( self, rank ):
    return any( c.rank==rank for rank in hand.cards )

This allows us to use a simpler in test for a given rank in a hand.

Similar design considerations...