常见的设计模式-单例模式

简述

实现了类在当前进程中只有一个实例，比如python-GC

重写__new__实现单例

class A:

    def __new__(cls, *args, **kwargs):

        if not hasattr(cls, '_instance'):
            cls._instance = super().__new__(cls, *args, **kwargs)
        return cls._instance
    pass
if __name__ == '__main__':
    a = A()
    b = A()
    print(id(a))
    print(id(b))

装饰器实现

def singleTon(cls, *args, **kw):

  instances = {}
  def inner():
    if cls not in instances:
      instances[cls] = cls(*args, **kw)
    return instances[cls]
  return inner

@singleTon
class A:
  pass