Wed Dec 26 16:00:00 GMT 2001

SingletonPattern

#: c01:SingletonPattern.py class OnlyOne: class __OnlyOne: def __init__(self, arg): self.val = arg def __str__(self): return `self` + self.val instance = None def __init__(self, arg): if not OnlyOne.instance: OnlyOne.instance = OnlyOne.__OnlyOne(arg) else: OnlyOne.instance.val = arg def __getattr__(self, name): return getattr(self.instance, name) x = OnlyOne('sausage') print x y = OnlyOne('eggs') print y z = OnlyOne('spam') print z print x print y print `x` print `y` print `z` output = ''' <__main__.__OnlyOne instance at 0076B7AC>sausage <__main__.__OnlyOne instance at 0076B7AC>eggs <__main__.__OnlyOne instance at 0076B7AC>spam <__main__.__OnlyOne instance at 0076B7AC>spam <__main__.__OnlyOne instance at 0076B7AC>spam <__main__.OnlyOne instance at 0076C54C> <__main__.OnlyOne instance at 0076DAAC> <__main__.OnlyOne instance at 0076AA3C> ''' #:~


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