基于元类
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| class Singleton(type):
def __init__(cls, *args, **kwargs):
""""""
cls.__instance = None
super().__init__(*args, **kwargs)
def __call__(cls, *args, **kwargs):
""""""
if cls.__instance is None:
cls.__instance = super().__call__(*args, **kwargs)
return cls.__instance
else:
return cls.__instance
class Spam(metaclass=Singleton):
...
s1 = Spam()
s2 = Spam()
print(id(s1))
print(id(s2))
|
基于 new 方法
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| class Singleton(object):
__instance = None
def __init__(self):
...
def __new__(cls, *args, **kwargs):
if not cls.__instance:
cls.__instance = super(Singleton, cls).__new__(cls, *args, **kwargs)
return cls.__instance
class Spam(Singleton):
...
s1 = Spam()
s2 = Spam()
print(id(s1))
print(id(s2))
|
基于装饰器
用闭包实现
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| def singleton(cls):
"""使用闭包的方式实现一个单例装饰器"""
__instance = {}
def _create(*args, **kwargs):
if cls not in __instance:
__instance[cls] = cls(*args, **kwargs)
return __instance[cls]
return _create
@singleton
class Spam(object):
...
s1 = Spam()
s2 = Spam()
print(id(s1))
print(id(s2))
|
用类实现
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| class Singleton(object):
def __init__(self, cls):
self.__cls = cls
self.__instance = {}
def __call__(self, *args, **kwargs):
if self.__cls not in self.__instance:
self.__instance[self.__cls] = self.__cls(*args, **kwargs)
return self.__instance[self.__cls]
@Singleton
class Spam(object):
...
s1 = Spam()
s2 = Spam()
print(id(s1))
print(id(s2))
|
注意
Python的模块是天然的单例模式
在一个py文件中, 多次导入同一个模块, 这个模块也只有在第一次的时候被导入, 后续的该模块导入语句都不会再执行了
参考链接
https://developer.aliyun.com/article/653759
