方法一：装饰器
利用“装饰器只会执行一次”这个特点
<code class="language-python hljs ">def singleton(cls): instances = []# 为什么这里不直接为None,因为内部函数没法访问外部函数的非容器变量 def getinstance(*args, **kwargs): if not instances: instances.append(cls(*args, **kwargs)) return instances[0] return getinstance@singletonclass Foo: a = 1f1 = Foo()f2 = Foo()print id(f1), id(f2)</code>
方法二：基类
利用“类变量对所有对象唯一”,即cls._instance
<code class="language-python hljs ">class Singleton(object): def __new__(cls, *args, **kwargs): if not hasattr(cls, ‘_instance‘): cls._instance = object.__new__(cls, *args, **kwargs) return cls._instanceclass Foo(Singleton): a = 1</code>
方法三：metaclass
利用“类变量对所有对象唯一”,即cls._instance
<code class="language-python hljs ">class Singleton(type): def __call__(cls, *args, **kwargs): if not hasattr(cls, ‘_instance‘): cls._instance = super(Singleton, cls).__call__(*args, **kwargs) return cls._instanceclass Foo(): __metaclass__ = Singleton</code>
方法四：Borg模式
利用“类变量对所有对象唯一”,即__share_state
<code class="language-python hljs ">class Foo: __share_state = {} def __init__(self): self.__dict__ = self.__share_state</code>方法五：利用import
利用“模块只会被import一次”
<code class="language-python hljs ">#在文件mysingleton中class Foo(object): passf = Foo()</code>
然后在其它模块，from mysingleton import f
直接拿f当作单例的对象来用