How Python uses Metaclass to implement singleton patterns

Source: Internet
Author: User

This article illustrates the way Python uses metaclass to implement singleton patterns. Share to everyone for your reference. The implementation methods are as follows:

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22-23 Class Singleton (type): Def __call__ (CLS, *args, **kwargs): print "Singleton call" if not hasattr (CLS, ' instance '): Cls.ins tance = Super (Singleton, CLS). __call__ (*args, **kwargs) return cls.instance def __new__ (CLS, name, bases, DCT): print "Sin Gleton new "Return type.__new__ (CLS, name, bases, DCT) def __init__ (CLS, name, bases, DCT): print" Singleton init "super (S Ingleton, CLS). __INIT__ (name, bases, DCT) class Cache (object): __metaclass__ = Singleton def __new__ (CLS, *args, **kwargs) : print "Cache new" return object.__new__ (CLS, *args, **kwargs) def __init__ (CLS, *args, **kwargs): print "Cache init" def __call__ (CLS, *args, **kwargs): print "Cache call" Print cache () print cache ()

Output:

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1 2 3 4 5 6 7 8 Singleton New Singleton init Singleton call cache new Cache init <__main__. Cache object at 0x01cdb130> Singleton call <__main__. Cache Object at 0x01cdb130>

I hope this article will help you with your Python programming.

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