单例模式

1 使用__new__方法

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): a = 1

2 共享属性

创建实例时把所有实例的__dict__指向同一个字典,这样它们具有相同的属性和方法.

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): a = 1

3 装饰器版本

def singleton(cls, *args, **kw): instances = {} def getinstance(): if cls not in instances: instances[cls] = cls(*args, **kw) return instances[cls] return getinstance @singleton class MyClass: ...

4 import方法

作为python的模块是天然的单例模式

# mysingleton.pyclass My_Singleton(object):    def foo(self): pass my_singleton = My_Singleton() # to use from mysingleton import my_singleton my_singleton.foo()