策略模式

网站参考：

https://sourcemaking.com/design_patterns/strategy

https://refactoringguru.cn/design-patterns/strategy/python/example#lang-features

代码参考：

"""Define a family of algorithms, encapsulate each one, and make theminterchangeable. Strategy lets the algorithm vary independently fromclients that use it."""import abcclass Context:    """    Define the interface of interest to clients.    Maintain a reference to a Strategy object.    """    def __init__(self, strategy):        self._strategy = strategy    def context_interface(self):        self._strategy.algorithm_interface()class Strategy(metaclass=abc.ABCMeta):    """    Declare an interface common to all supported algorithms. Context    uses this interface to call the algorithm defined by a    ConcreteStrategy.    """    @abc.abstractmethod    def algorithm_interface(self):        passclass ConcreteStrategyA(Strategy):    """    Implement the algorithm using the Strategy interface.    """    def algorithm_interface(self):        passclass ConcreteStrategyB(Strategy):    """    Implement the algorithm using the Strategy interface.    """    def algorithm_interface(self):        passdef main():    concrete_strategy_a = ConcreteStrategyA()    context = Context(concrete_strategy_a)    context.context_interface()if __name__ == "__main__":    main()

上述除了学习了设计模式，还学习到了抽象基类：

1）class Strategy(metaclass=abc.ABCMeta) 抽象基类只能被继承，不能被实例化

2）@abc.abstractmethod 当抽象基类中出现这个装饰器意味着子类中这个方法必须实现