在python中怎么实现单例模式？下面给大家带来七种不同的方法：

一：staticmethod

代码如下：

class Singleton(object): instance = None def __init__(self): raise SyntaxError('can not instance, please use get_instance') def get_instance(): if Singleton.instance is None: Singleton.instance = object.__new__(Singleton) return Singleton.instancea = Singleton.get_instance()b = Singleton.get_instance()print('a id=', id(a))print('b id=', id(b))

该方法的要点是在__init__抛出异常，禁止通过类来实例化，只能通过静态get_instance函数来获取实例；因为不能通过类来实例化，所以静态get_instance函数中可以通过父类object.__new__来实例化。

二：classmethod

和方法一类似，代码：

class Singleton(object): instance = None def __init__(self): raise SyntaxError('can not instance, please use get_instance') def get_instance(cls): if Singleton.instance is None: Singleton.instance = object.__new__(Singleton) return Singleton.instancea = Singleton.get_instance()b = Singleton.get_instance()print('a id=', id(a))print('b id=', id(b))

该方法的要点是在__init__抛出异常，禁止通过类来实例化，只能通过静态get_instance函数来获取实例；因为不能通过类来实例化，所以静态get_instance函数中可以通过父类object.__new__来实例化。

三：类属性方法

和方法一类似， 代码：

class Singleton(object): instance = None def __init__(self): raise SyntaxError('can not instance, please use get_instance') def get_instance(): if Singleton.instance is None: Singleton.instance = object.__new__(Singleton) return Singleton.instancea = Singleton.get_instance()b = Singleton.get_instance()print(id(a))print(id(b))

该方法的要点是在__init__抛出异常，禁止通过类来实例化，只能通过静态get_instance函数来获取实例；因为不能通过类来实例化，所以静态get_instance函数中可以通过父类object.__new__来实例化。

四：__new__

常见的方法， 代码如下：

class Singleton(object): instance = None def __new__(cls, *args, **kw): if not cls.instance: # cls.instance = object.__new__(cls, *args) cls.instance = super(Singleton, cls).__new__(cls, *args, **kw) return cls.instancea = Singleton()b = Singleton()print(id(a))print(id(b))

五：装饰器

代码如下：

def Singleton(cls): instances = {} def getinstance(): if cls not in instances: instances[cls] = cls() return instances[cls] return getinstanceclass MyClass: passa = MyClass()b = MyClass()c = MyClass()print(id(a))print(id(b))print(id(c))

六：元类

python2版：

class Singleton(type): def __init__(cls, name, bases, dct): super(Singleton, cls).__init__(name, bases, dct) cls.instance = None def __call__(cls, *args): if cls.instance is None: cls.instance = super(Singleton, cls).__call__(*args) return cls.instanceclass MyClass(object): __metaclass__ = Singletona = MyClass()b = MyClass()c = MyClass()print(id(a))print(id(b))print(id(c))print(a is b)print(a is c)

或者：

class Singleton(type): def __new__(cls, name, bases, attrs): attrs["_instance"] = None return super(Singleton, cls).__new__(cls, name, bases, attrs) def __call__(cls, *args, **kwargs): if cls._instance is None: cls._instance = super(Singleton, cls).__call__(*args, **kwargs) return cls._instanceclass Foo(object): __metaclass__ = Singletonx = Foo()y = Foo()print(id(x))print(id(y))

python3版：

class Singleton(type): def __new__(cls, name, bases, attrs): attrs['instance'] = None return super(Singleton, cls).__new__(cls, name, bases, attrs) def __call__(cls, *args, **kwargs): if cls.instance is None: cls.instance = super(Singleton, cls).__call__(*args, **kwargs) return cls.instanceclass Foo(metaclass=Singleton): passx = Foo()y = Foo()print(id(x))print(id(y))

七：名字覆盖

代码如下：

class Singleton(object): def foo(self): print('foo') def __call__(self): return selfSingleton = Singleton()Singleton.foo()a = Singleton()b = Singleton()print(id(a))print(id(b))

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