单例模式
所谓单例,是指一个类的实例从始至终只能被创建一次。以后调用只调用他一个
----类
----__new__
----元类metaclass
----文件
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import time import threading class Singleton(object): _instance_lock = threading.Lock() def __init__(self): time.sleep(1) @classmethod def instance(cls, *args, **kwargs): if not hasattr(Singleton, "_instance"): with Singleton._instance_lock: if not hasattr(Singleton, "_instance"): Singleton._instance = Singleton(*args, **kwargs) return Singleton._instance 使用先说明,以后用单例模式,obj = Singleton.instance() 示例: obj1 = Singleton.instance() obj2 = Singleton.instance() print(obj1,obj2) 错误示例 obj1 = Singleton() obj2 = Singleton() print(obj1,obj2)
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import time import threading class Singleton(object): _instance_lock = threading.Lock() def __init__(self): pass def __new__(cls, *args, **kwargs): if not hasattr(Singleton, "_instance"): with Singleton._instance_lock: if not hasattr(Singleton, "_instance"): Singleton._instance = object.__new__(cls, *args, **kwargs) return Singleton._instance # 使用先说明,以后用单例模式,obj = Singleton() # 示例 # obj1 = Singleton() # obj2 = Singleton() # print(obj1,obj2)
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import threading class SingletonType(type): _instance_lock = threading.Lock() def __call__(cls, *args, **kwargs): if not hasattr(cls, "_instance"): with SingletonType._instance_lock: if not hasattr(cls, "_instance"): cls._instance = super(SingletonType,cls).__call__(*args, **kwargs) return cls._instance class Foo(metaclass=SingletonType): def __init__(self,name): self.name = name obj1 = Foo('name') obj2 = Foo('name') print(obj1,obj2)
PS: 为了保证线程安全在内部加入锁
其实,Python 的模块就是天然的单例模式,因为模块在第一次导入时,会生成 .pyc
文件,当第二次导入时,就会直接加载 .pyc
文件,而不会再次执行模块代码。因此,我们只需把相关的函数和数据定义在一个模块中,就可以获得一个单例对象了。如果我们真的想要一个单例类,可以考虑这样做:
# mysingleton.py class My_Singleton(object): def foo(self): pass my_singleton = My_Singleton()
将上面的代码保存在文件 mysingleton.py
中,然后这样使用:
from mysingleton import my_singleton my_singleton.foo()
追加:
最简单的方法:
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class singleton( object ): pass singleton = singleton() |
将名字singleton绑定到实例上,singleton就是它自己类的唯一对象了。
转载请注来源:https://github.com/fugui0310