使用__new__方法

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class Singleton(object):

    def __new__(cls, *args, **kw):

        if not hasattr(cls, '_instance'):

            orig = super(Singleton, cls)

            cls._instance = orig.__new__(cls, *args, **kw)

        return cls._instance



class MyClass(Singleton):

    pass

共享属性

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class Borg(object):

    _state = {}

    def __new__(cls, *args, **kw):

        ob = super(Borg, cls).__new__(cls, *args, **kw)

        ob.__dict__ = cls._state

        return ob



class MyClass2(Borg):

    pass

装饰器版本

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def singleton(cls):

    instances = {}

    def getinstance(*args, **kw):

        if cls not in instances:

            instances[cls] = cls(*args, **kw)

        return instances[cls]

    return getinstance



@singleton

class MyClass:

    pass

import方法

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# mysingleton.py

class My_Singleton(object):

    def foo(self):

        pass



my_singleton = My_Singleton()



# to use

from mysingleton import my_singleton



my_singleton.foo()