常用的单例模式

单例模式的实现

• 使用 new方法

  class Singleton(object):
      def __new__(cls, *args, **kw):
          if not hasattr(cls, '_instance'):
              orig = super(Singleton, cls)
              cls._instance = orig.__new__(cls, *args, **kw)
          return cls._instance
  
  class MyClass(Singleton):
      a = 1
  

• 共享属性

  创建实例时把所有实例的dict指向一个字典，这样它们就具有相同的属性和方法

  class Borg(object):
      _state = {}
      def __new__(cls, *args, **kw):
          ob = super(Borg, cls).__new__(cls, *args, **kw)
          ob.__dict__ = cls._state
          return ob
  
  class MyClass2(Borg):
      a = 1
  

• 装饰器版本

  def singleton(cls, *args, **kw):
      instances = {}
      def getinstance():
          if cls not in instances:
              instances[cls] = cls(*args, **kw)
          return instances[cls]
      return getinstance
  
  @singleton
  class MyClass:
    ...
  

• import方法

  作为python的模块是天然的单例模式

  # mysingleton.py
  class My_Singleton(object):
      def foo(self):
          pass
  
  my_singleton = My_Singleton()
  
  # to use
  from mysingleton import my_singleton
  
  my_singleton.foo()