Python uses metaclass to implement the Singleton Mode

Python uses metaclass to implement the Singleton Mode

This example describes how Python uses metaclass to implement the Singleton mode. Share it with you for your reference. The specific implementation method is as follows:

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Class Singleton (type ): Def _ call _ (cls, * args, ** kwargs ): Print "Singleton call" If not hasattr (cls, 'instance '): Cls. instance = super (Singleton, cls). _ call _ (* args, ** kwargs) Return cls. instance Def _ new _ (cls, name, bases, dct ): Print "Singleton new" Return type. _ new _ (cls, name, bases, dct) Def _ init _ (cls, name, bases, dct ): Print "Singleton init" Super (Singleton, 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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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 Python programming.