飘逸的python

方法一：装饰器

利用“装饰器只会执行一次”这个特点

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

@singleton
class Foo:
    a = 1

f1 = Foo()
f2 = Foo()
print id(f1), id(f2)

方法二：基类

利用“类变量对所有对象唯一”,即cls._instance

class Singleton(object):
    def __new__(cls, *args, **kwargs):
        if not hasattr(cls, '_instance'):
            cls._instance = object.__new__(cls, *args, **kwargs)
        return cls._instance

class Foo(Singleton):
    a = 1

方法三：metaclass

利用“类变量对所有对象唯一”,即cls._instance

class Singleton(type):
    def __call__(cls, *args, **kwargs):
        if not hasattr(cls, '_instance'):
            cls._instance = super(Singleton, cls).__call__(*args, **kwargs)
        return cls._instance

class Foo():
    __metaclass__ = Singleton

方法四：Borg模式

利用“类变量对所有对象唯一”,即__share_state

class Foo:
   __share_state = {}
   def __init__(self):
       self.__dict__ = self.__share_state

方法五：利用import

利用“模块只会被import一次”

#在文件mysingleton中
class Foo(object):
     pass

f = Foo()

然后在其它模块，from mysingleton import f 
直接拿f当作单例的对象来用

 

 转自:http://blog.csdn.net/handsomekang/article/details/46672047