python如何实现单例模式？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.instance a = 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.instance a = 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.instance a = 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, IT之家args, IT之家IT之家kw): if not cls.instance: # cls.instance = object.__new__(cls, IT之家args) cls.instance = super(Singleton, cls).__new__(cls, IT之家args, IT之家IT之家kw) return cls.instance a = Singleton() b = Singleton() print(id(a)) print(id(b))

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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 getinstance class MyClass: pass a = 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, IT之家args): if cls.instance is None: cls.instance = super(Singleton, cls).__call__(IT之家args) return cls.instance class MyClass(object): __metaclass__ = Singleton a = 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, IT之家args, IT之家IT之家kwargs): if cls._instance is None: cls._instance = super(Singleton, cls).__call__(IT之家args, IT之家IT之家kwargs) return cls._instance class Foo(object): __metaclass__ = Singleton x = 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, IT之家args, IT之家IT之家kwargs): if cls.instance is None: cls.instance = super(Singleton, cls).__call__(IT之家args, IT之家IT之家kwargs) return cls.instance class Foo(metaclass=Singleton): pass x = 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 self Singleton = Singleton() Singleton.foo() a = Singleton() b = Singleton() print(id(a)) print(id(b))

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