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 them
interchangeable. Strategy lets the algorithm vary independently from
clients that use it.
"""

import abc


class 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):
        pass


class ConcreteStrategyA(Strategy):
    """
    Implement the algorithm using the Strategy interface.
    """

    def algorithm_interface(self):
        pass


class ConcreteStrategyB(Strategy):
    """
    Implement the algorithm using the Strategy interface.
    """

    def algorithm_interface(self):
        pass


def 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