设计模式-创建型模式之单例

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))