class Deck

Now we define our Deck and Hand classes by inheriting from this CardCollection base class. The mechanism to show inheritance in Python is simply to include the base class name in parentheses after the derived class name,

 1 class Deck(CardCollection):
 2     # Override ancestor's constructor, i.e. replace the default.
 3     def __init__(self):
 4         self.cards = []
 5         for cardnum in range(52):
 6             self.add( Card(cardnum) )
 7
 8     # Alias the inherited method "size" as "cards_left",
 9     # because we usually ask how many cards are left in a
10     # deck rather than asking about its size.
11     def cards_left(self):
12         return self.size()
13 
14     # Another alias. When using a deck of cards we talk about "dealing"
15     # cards not "removing" them from the deck.
16     def deal(self):
17         return self.remove()
18
19     # Add a new method, shuffle, that does not exist in ancestor class.
20     def shuffle(self):
21         for i in range(  2*self.size() ):
22             self.cards.insert(random.randrange(len(self.cards)), self.cards.pop())

This example shows most of what you can do with inheritance:

→ line 1

The syntax to define a class Deck that inherits from the class CardCollection. Jargon: Deck is the derived or descendant class; CardCollection is the base class, superclass or ancestor class.

→ lines 3-6

Replace a method from the base class with a customized version. This is just done by redefining the method, i.e. if you use the same name in the derived class it hides the version in the base class. The jargon for this is specialization because we specialize the operation of the method for our derived class' characteristics.

→ lines 11-12

We provide an "alias", i.e. a more meaningful name, for a method in the base class. In this case we can refer to cards_left() instead of size(). Note that this is not a renaming; it is providing a second name. We can still access the method size() if we wish.

→ lines 16-17

Another alias, this time allowing us to refer to the method remove by the name deal.

→ lines 20-22

We can add new methods in the derived class that do not exist in the base class. In this case we add a shuffle method to our derived class. Note that inheritance is one way: we cannot call the shuffle method on a CardCollection object only on a Deck object. The jargon for this is augmentation since we are augmenting the functionality of our base class.