IT公司面试手册

Python有两种方式可以实现单例模式，下面两个例子使用了不同的方式实现单例模式：
1.
class Singleton(type):
def __init__(cls, name, bases, dict):
super(Singleton, cls).__init__(name, bases, dict)
cls.instance = None

def __call__(cls, *args, **kw):
if cls.instance is None:
cls.instance = super(Singleton, cls).__call__(*args, **kw)

return cls.instance

class MyClass(object):
__metaclass__ = Singleton

print MyClass()
print MyClass()
2. 使用decorator来实现单例模式
def singleton(cls):
instances = {}
def getinstance():
if cls not in instances:
instances[cls] = cls()
return instances[cls]
return getinstance

@singleton
class MyClass:
…