[Tutor] Okay, something's funky

[Jacob S.]

Hi everyone. Very simple set up for the problem, strange problem.

####  Cards.py ###
## Taken almost directly from Thinking Like a Computer Scientist
class Card:
    suitList = ["Clubs","Diamonds","Hearts","Spades"]
    rankList = 
["","Ace","2","3","4","5","6","7","8","9","10","Jack","Queen","King"]

    def __init__(self,suit,rank):
        self.suit = suit
        self.rank = rank
    def __repr__(self):
        return str(self)
    def __str__(self):
        return "%s of %s" % 
(self.rankList[self.rank],self.suitList[self.suit])
    def __cmp__(self,other):
        if self.suit > other.suit: return 1
        if self.suit < other.suit: return -1
        if self.rank > other.rank: return 1
        if self.rank < other.rank: return -1
        return 0

class Deck:
    def __init__(self):
        self.cards = []
        for suit in range(4):
            for rank in range(1,14):
                self.cards.append(Card(suit,rank))
    def __str__(self):
        for card in self.cards:
            print card

### End of Cards.py ###

Nothing wrong, right?
So I fire up the interpreter and enter these commands

Python 2.4 (#60, Nov 30 2004, 11:49:19) [MSC v.1310 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> from Cards import *
>>> a = Deck()
>>> print a
Ace of Clubs
2 of Clubs
3 of Clubs
4 of Clubs
5 of Clubs
6 of Clubs
7 of Clubs
8 of Clubs
9 of Clubs
10 of Clubs
Jack of Clubs
Queen of Clubs
King of Clubs
Ace of Diamonds
2 of Diamonds
3 of Diamonds
4 of Diamonds
5 of Diamonds
6 of Diamonds
7 of Diamonds
8 of Diamonds
9 of Diamonds
10 of Diamonds
Jack of Diamonds
Queen of Diamonds
King of Diamonds
Ace of Hearts
2 of Hearts
3 of Hearts
4 of Hearts
5 of Hearts
6 of Hearts
7 of Hearts
8 of Hearts
9 of Hearts
10 of Hearts
Jack of Hearts
Queen of Hearts
King of Hearts
Ace of Spades
2 of Spades
3 of Spades
4 of Spades
5 of Spades
6 of Spades
7 of Spades
8 of Spades
9 of Spades
10 of Spades
Jack of Spades
Queen of Spades
King of Spades
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: __str__ returned non-string (type NoneType)
>>>Python 2.4 (#60, Nov 30 2004, 11:49:19) [MSC v.1310 32 bit (Intel)] on 
>>>win32
Type "help", "copyright", "credits" or "license" for more information.
>>> from Cards import *
>>> a = Deck()
>>> print a
Ace of Clubs
2 of Clubs
3 of Clubs
4 of Clubs
5 of Clubs
6 of Clubs
7 of Clubs
8 of Clubs
9 of Clubs
10 of Clubs
Jack of Clubs
Queen of Clubs
King of Clubs
Ace of Diamonds
2 of Diamonds
3 of Diamonds
4 of Diamonds
5 of Diamonds
6 of Diamonds
7 of Diamonds
8 of Diamonds
9 of Diamonds
10 of Diamonds
Jack of Diamonds
Queen of Diamonds
King of Diamonds
Ace of Hearts
2 of Hearts
3 of Hearts
4 of Hearts
5 of Hearts
6 of Hearts
7 of Hearts
8 of Hearts
9 of Hearts
10 of Hearts
Jack of Hearts
Queen of Hearts
King of Hearts
Ace of Spades
2 of Spades
3 of Spades
4 of Spades
5 of Spades
6 of Spades
7 of Spades
8 of Spades
9 of Spades
10 of Spades
Jack of Spades
Queen of Spades
King of Spades
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: __str__ returned non-string (type NoneType)
>>>Python 2.4 (#60, Nov 30 2004, 11:49:19) [MSC v.1310 32 bit (Intel)] on 
>>>win32
Type "help", "copyright", "credits" or "license" for more information.
>>> from Cards import *
>>> a = Deck()
>>> print a
Ace of Clubs
2 of Clubs
3 of Clubs
4 of Clubs
5 of Clubs
6 of Clubs
7 of Clubs
8 of Clubs
9 of Clubs
10 of Clubs
Jack of Clubs
Queen of Clubs
King of Clubs
Ace of Diamonds
2 of Diamonds
3 of Diamonds
4 of Diamonds
5 of Diamonds
6 of Diamonds
7 of Diamonds
8 of Diamonds
9 of Diamonds
10 of Diamonds
Jack of Diamonds
Queen of Diamonds
King of Diamonds
Ace of Hearts
2 of Hearts
3 of Hearts
4 of Hearts
5 of Hearts
6 of Hearts
7 of Hearts
8 of Hearts
9 of Hearts
10 of Hearts
Jack of Hearts
Queen of Hearts
King of Hearts
Ace of Spades
2 of Spades
3 of Spades
4 of Spades
5 of Spades
6 of Spades
7 of Spades
8 of Spades
9 of Spades
10 of Spades
Jack of Spades
Queen of Spades
King of Spades
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: __str__ returned non-string (type NoneType)
>>>Python 2.4 (#60, Nov 30 2004, 11:49:19) [MSC v.1310 32 bit (Intel)] on 
>>>win32
Type "help", "copyright", "credits" or "license" for more information.
>>> from Cards import *
>>> a = Deck()
>>> print a
Ace of Clubs
2 of Clubs
3 of Clubs
4 of Clubs
5 of Clubs
6 of Clubs
7 of Clubs
8 of Clubs
9 of Clubs
10 of Clubs
Jack of Clubs
Queen of Clubs
King of Clubs
Ace of Diamonds
2 of Diamonds
3 of Diamonds
4 of Diamonds
5 of Diamonds
6 of Diamonds
7 of Diamonds
8 of Diamonds
9 of Diamonds
10 of Diamonds
Jack of Diamonds
Queen of Diamonds
King of Diamonds
Ace of Hearts
2 of Hearts
3 of Hearts
4 of Hearts
5 of Hearts
6 of Hearts
7 of Hearts
8 of Hearts
9 of Hearts
10 of Hearts
Jack of Hearts
Queen of Hearts
King of Hearts
Ace of Spades
2 of Spades
3 of Spades
4 of Spades
5 of Spades
6 of Spades
7 of Spades
8 of Spades
9 of Spades
10 of Spades
Jack of Spades
Queen of Spades
King of Spades
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: __str__ returned non-string (type NoneType)
>>> a.cards
[Ace of Clubs, 2 of Clubs, 3 of Clubs, 4 of Clubs, 5 of Clubs, 6 of Clubs, 7 
of
Clubs, 8 of Clubs, 9 of Clubs, 10 of Clubs, Jack of Clubs, Queen of Clubs, 
King
of Clubs, Ace of Diamonds, 2 of Diamonds, 3 of Diamonds, 4 of Diamonds, 5 of 
Dia
monds, 6 of Diamonds, 7 of Diamonds, 8 of Diamonds, 9 of Diamonds, 10 of 
Diamond
s, Jack of Diamonds, Queen of Diamonds, King of Diamonds, Ace of Hearts, 2 
of He
arts, 3 of Hearts, 4 of Hearts, 5 of Hearts, 6 of Hearts, 7 of Hearts, 8 of 
Hear
ts, 9 of Hearts, 10 of Hearts, Jack of Hearts, Queen of Hearts, King of 
Hearts,
Ace of Spades, 2 of Spades, 3 of Spades, 4 of Spades, 5 of Spades, 6 of 
Spades,
7 of Spades, 8 of Spades, 9 of Spades, 10 of Spades, Jack of Spades, Queen 
of Sp
ades, King of Spades]
>>> for card in a.cards:
...     print card
...
Ace of Clubs
2 of Clubs
3 of Clubs
4 of Clubs
5 of Clubs
6 of Clubs
7 of Clubs
8 of Clubs
9 of Clubs
10 of Clubs
Jack of Clubs
Queen of Clubs
King of Clubs
Ace of Diamonds
2 of Diamonds
3 of Diamonds
4 of Diamonds
5 of Diamonds
6 of Diamonds
7 of Diamonds
8 of Diamonds
9 of Diamonds
10 of Diamonds
Jack of Diamonds
Queen of Diamonds
King of Diamonds
Ace of Hearts
2 of Hearts
3 of Hearts
4 of Hearts
5 of Hearts
6 of Hearts
7 of Hearts
8 of Hearts
9 of Hearts
10 of Hearts
Jack of Hearts
Queen of Hearts
King of Hearts
Ace of Spades
2 of Spades
3 of Spades
4 of Spades
5 of Spades
6 of Spades
7 of Spades
8 of Spades
9 of Spades
10 of Spades
Jack of Spades
Queen of Spades
King of Spades
>>> len(a.cards)
52
>>>

Why am I getting a NoneType in my loop?

Any help appreciated.
Jacob