# 使用基类new

class Singleton(object):

_instance = None

def __new__(cls, *args, **kwargs):

if not hasattr(cls, '_instance'):

cls._instance = super(Singleton,

cls).__new__(cls, *args, **kwargs)

return cls._instance

class Foo(Singleton):

pass

foo1 = Foo()

foo2 = Foo()

print(foo1 is foo2)

# 使用装饰器

from functools import wraps

def singleton(cls):

instances = {}

def wrapper(*args, **kwargs):

if cls not in instances:

instances[cls] = cls(*args, **kwargs)

return instances[cls]

return wrapper

@singleton

class FOO(object):

pass

foo3 = FOO()

foo4 = FOO()

print(foo3 is foo4)