# coding=utf-8
"""
单列模式的几种实现方法
"""
class Singleton(object):
_instance = None
def __new__(cls, *args, **kwargs):
# __new__ 方法在创建对象过程中检查类属性_instance是否为空，不为空就直接返回
if cls._instance:
return cls._instance
cls._instance = cv = object.__new__(cls, *args, **kwargs)
return cv
def __init__(self, v):
"""单列方法不应该有此方法"""
self.v = v
class Singleton1(object):
"""
这不是一个严格单列类 因为：
s1 = Singleton(1)
s2 = Singleton(2)
print s1 is s2 ＃ False
"""
_state = {}
def __new__(cls, *args, **kargs):
instance = object.__new__(cls, *args, **kargs)
instance.__dict__ = cls._state
return instance
def __init__(self, v):
self.v = v
class SingletonMetaClass(type):
"""单列模式元类"""
def __init__(cls, name, bases, dict):
super(SingletonMetaClass, cls).__init__(name, bases, dict)
cls._instance = None
def __call__(cls, *args, **kargs):
if cls._instance is None:
cls._instance = super(SingletonMetaClass, cls).__call__(*args, **kargs)
return cls._instance
class SingletonWithMeta(object):
"""基于元类的单列类"""
__metaclass__ = SingletonMetaClass
def __init__(self, v):
self.v = v
def singleton_decorator(cls):
"""单列描述类"""
instances = {}
def _singleton(*args, **kw):
# print args
if cls not in instances:
instances[cls] = cls(*args, **kw)
return instances[cls]
return _singleton
@singleton_decorator
class SingletonWithDecorator(object):
a = 1
def __init__(self, v=0):
self.v = v
if __name__ == "__main__":
s1 = Singleton(1)
s2 = Singleton(2)
print s1 is s2
print s1.v, s2.v
s3 = Singleton1(3)
s4 = Singleton1(4)
print s3 is s4
print s3.v, s4.v
s5 = SingletonWithMeta(5)
s6 = SingletonWithMeta(6)
print s5 is s6
print s5.v, s6.v
s7 = SingletonWithDecorator(7)
s8 = SingletonWithDecorator(8)
print s7 is s8
print s7.v, s8.v
