Python实现单例模式的5种方法

时间:2022-06-04 04:01:21

基本介绍

一个对象只允许被一次创建,一个类只能创建一个对象,并且提供一个全局访问点。

单例模式应该是应用最广泛,实现最简单的一种创建型模式。

特点:全局唯一,允许更改

优缺点

优点:

  • 避免对资源的多重占用,如写入文件操作
  • 节省内存
  • 防止命名空间被污染

缺点:

  • 没有接口,不能继承,与单一职责原则冲突,一个类应该只关心内部逻辑,而不关心外面怎么样来实例化

Python实现

方式1,元类实现:

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class MetaClass(type):
    def __call__(self, *args, **kwargs):
        """
        self : class Singleton
        """
        if not hasattr(self, "ins"):
            insObject = super(__class__, self).__call__(*args, **kwargs)
            setattr(self, "ins", insObject)
        return getattr(self, "ins")
 
 
class Singleton(object, metaclass=MetaClass):
    pass
 
 
if __name__ == "__main__":
    ins = Singleton()
    print(id(ins))
    ins = Singleton()
    print(id(ins))

方式2,继承实现:

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class ParentClass:
    def __new__(cls, *args, **kwargs) -> object:
        """
        cls : class Singeton
        """
        if not hasattr(cls, "ins"):
            insObject = super(__class__, cls).__new__(cls, *args, **kwargs)
            setattr(cls, "ins", insObject)
        return getattr(cls, "ins")
 
 
class Singleton(ParentClass):
    pass
 
 
if __name__ == "__main__":
    ins = Singleton()
    print(id(ins))
    ins = Singleton()
    print(id(ins))

方式3,装饰器实现:

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def warpper(clsObject):
    def inner(*args, **kwargs):
        if not hasattr(clsObject, "ins"):
            insObject = clsObject(*args, **kwargs)
            setattr(clsObject, "ins", insObject)
        return getattr(clsObject, "ins")
    return inner
 
 
@warpper
class Singleton:
    pass
 
 
if __name__ == "__main__":
    ins = Singleton()
    print(id(ins))
    ins = Singleton()
    print(id(ins))

方式4,模块实现:

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- foo.py --> ins = Singleton()
- bar.py --> from foo import ins

方式5,@classmethod实现单例模式:

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class Singleton:
 
    @classmethod
    def getSingletonInstanceObject(cls, *args, **kwargs):
        if not hasattr(cls, "ins"):
            insObject = cls(*args, **kwargs)
            setattr(cls, "ins", insObject)
        return getattr(cls, "ins")
 
 
if __name__ == "__main__":
    ins = Singleton.getSingletonInstanceObject()
    print(id(ins))
    ins = Singleton.getSingletonInstanceObject()
    print(id(ins))

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原文链接:https://www.cnblogs.com/Yunya-Cnblogs/p/14880267.html