设计模式-创建型模式之单例

2023-03-13

self args cls

1、元类实现1classSingleton(type):2def__init__(self,*args,**kwargs):3super().__init__(*args,**kwargs)4self._instance=None56#重写__call__7def__call__(self,*arg

1、元类实现

 1 class Singleton(type):
 2     def __init__(self, *args, **kwargs):
 3         super().__init__(*args, **kwargs)
 4         self._instance = None
 5 
 6     # 重写__call__
 7     def __call__(self, *args, **kwargs):
 8         if not self._instance:
 9             self._instance = super().__call__(*args, **kwargs)
10         return self._instance
11 
12 
13 class Valley(metaclass=Singleton):
14     ...
15 
16 
17 a = Valley()
18 b = Valley()
19 print(id(a), id(b))

2、装饰器实现

 1 def singleton(cls):
 2     _instance = {}
 3 
 4     def wrapper(*args, **kwargs):
 5         if cls not in _instance:
 6             _instance[cls] = cls(*args, **kwargs)
 7         return _instance[cls]
 8 
 9     return wrapper
10 
11 
12 @singleton
13 class Valley():
14     ...
15 
16 
17 a = Valley()
18 b = Valley()
19 print(id(a), id(b))

3、重写new

　　前面两种方式是之前记录的，通过继承或者装饰器来实现，相对可能要复杂点，最近发现一种方式是可以直接在类的内部实现，重写__new__双下方法

 1 class Valley:
 2     _instance = None
 3 
 4     def __new__(cls, *args, **kwargs):
 5         if cls._instance is None:
 6             cls._instance = super().__new__(cls, *args, **kwargs)
 7         return cls._instance
 8 
 9 
10 if __name__ == '__main__':
11     a = Valley()
12     b = Valley()
13     print(id(a), id(b))