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Python 单例

2024-09-21 04:39:12   215人阅读

方法一

　　实现__new__方法，然后将类的一个实例绑定到类变量_instance上；如果cls._instance为None，则说明该类还没有被实例化过，new一个该类的实例，并返回；如果cls._instance不为None，直接返回_instance，代码如下

class Singleton(object):    def __new__(cls, *args, **kwargs):    if not hasattr(cls, ‘_instance‘):      orig = super(Singleton, cls)      cls._instance = orig.__new__(cls, *args, **kwargs)    return cls._instance  class MyClass(Singleton):  a = 1  one = MyClass()two = MyClass()  #one和two完全相同,可以用id(), ==, is检测print id(one)  # 29097904print id(two)  # 29097904print one == two  # Trueprint one is two  # True

方法二

　　本质上是方法一的升级版，使用__metaclass__（元类）的高级python用法，具体代码如下：

class Singleton2(type):    def __init__(cls, name, bases, dict):    super(Singleton2, cls).__init__(name, bases, dict)    cls._instance = None    def __call__(cls, *args, **kwargs):    if cls._instance is None:      cls._instance = super(Singleton2, cls).__call__(*args, **kwargs)    return cls._instance  class MyClass2(object):  __metaclass__ = Singleton2  a = 1  one = MyClass2()two = MyClass2()  print id(one)  # 31495472print id(two)  # 31495472print one == two  # Trueprint one is two  # True

方法三

　　使用Python的装饰器(decorator)实现单例模式，这是一种更Pythonic的方法；单利类本身的代码不是单例的，通装饰器使其单例化，代码如下：

　　

def singleton(cls, *args, **kwargs):  instances = {}  def _singleton():    if cls not in instances:      instances[cls] = cls(*args, **kwargs)    return instances[cls]  return _singleton  @singletonclass MyClass3(object):  a = 1  one = MyClass3()two = MyClass3()  print id(one)  # 29660784print id(two)  # 29660784print one == two  # Trueprint one is two  # True

 

　　

 

Python 单例


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