flyweight.py

'''http://codesnipers.com/?q=python-flyweights'''

import weakref 

class Card(object):
 '''The object pool. Has builtin reference counting'''
 _CardPool = weakref.WeakValueDictionary() 

 '''Flyweight implementation. If the object exists in the
 pool just return it (instead of creating a new one)'''
 def __new__(cls, value, suit): 
 obj = Card._CardPool.get(value + suit, None) 
 if not obj: 
 obj = object.__new__(cls) 
 Card._CardPool[value + suit] = obj 
 obj.value, obj.suit = value, suit 
 return obj

 # def __init__(self, value, suit): 
 # self.value, self.suit = value, suit 

 def __repr__(self): 
 return "<Card: %s%s>" % (self.value, self.suit) 

if __name__ == '__main__':
 # comment __new__ and uncomment __init__ to see the difference
 c1 = Card('9', 'h')
 c2 = Card('9', 'h')
 print(c1, c2)
 print(c1 == c2)
 print(id(c1), id(c2))