python-patterns/flyweight.py at master · lockys/python-patterns · GitHub

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#!/usr/bin/env python

# -*- coding: utf-8 -*-

"""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))

### OUTPUT ###

# <Card: 9h> <Card: 9h>

# True

# 140368617673296 140368617673296

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