Question

Possible Duplicate:
“Least Astonishment” in Python: The Mutable Default Argument
dictionary shared between objects for no reason?

     class Player():
        zones = {}
        def __init__(self):
            self.zones['hand'] = []
        def InitHand(self):
            for a in range(5):
                self.zones['hand'].append(a)
lst = []
lst.append(Player())
lst.append(Player())
lst[0].InitHand()
print lst[1].zones['hand']

This prints “[0, 1, 2, 3, 4]”, but I only initialized the 0th element…
Changing them to arrays as below fixes the problem, but for the life of me I can’t figure out why this happens.

    class Player2():
        zones = []
        def __init__(self):
            self.zones = []
        def InitHand(self):
            for a in range(5):
                self.zones.append(a)
lst = []
lst.append(Player2())
lst.append(Player2())
lst[0].InitHand()
print lst[1].zones

This prints “[]” as expected

Answer 1

In your code, all players share the same zones dictionary. Anything set in the class scope is a class attribute, not an instance attribute.

class Player():
    def __init__(self):
        self.zones = {}
        self.zones['hand'] = []
    def InitHand(self):
        for a in range(5):
            self.zones['hand'].append(a)