飘逸的python - 单例模式乱弹

 1 def singleton(cls):
 2     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
 3     def getinstance(*args, **kwargs):
 4         if not instances:
 5             instances.append(cls(*args, **kwargs))
 6         return instances[0]
 7     return getinstance
 8 
 9 @singleton
10 class Foo:
11     a = 1
12 
13 f1 = Foo()
14 f2 = Foo()
15 print id(f1), id(f2)

1 class Singleton(object):
2     def __new__(cls, *args, **kwargs):
3         if not hasattr(cls, ‘_instance‘):
4             cls._instance = object.__new__(cls, *args, **kwargs)
5         return cls._instance
6 
7 class Foo(Singleton):
8     a = 1

1 class Singleton(type):
2     def __call__(cls, *args, **kwargs):
3         if not hasattr(cls, ‘_instance‘):
4             cls._instance = super(Singleton, cls).__call__(*args, **kwargs)
5         return cls._instance
6 
7 class Foo():
8     __metaclass__ = Singleton

1 class Foo:
2    __share_state = {}
3    def __init__(self):
4        self.__dict__ = self.__share_state

1 #在文件mysingleton中
2 class Foo(object):
3      pass
4 
5 f = Foo()