基于Python学习《Head First设计模式》第一章策略模式

抽象超类Animal

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from abc import ABC, abstractmethod# 方式一
# class Animal:
#
#     def make_sound(self):
#         raise NotImplementedError('子类必须实现make_sound方法')# 方式二
class Animal(ABC):"""抽象类"""@abstractmethoddef make_sound(self):"""子类必须实现该方法，表示所有动物都能发出声音"""passclass Dog(Animal):def make_sound(self):self._bark()def _bark(self):  # 单下划线表示仅内部调用，相当于java的privateprint("汪汪叫")class Cat(Animal):def make_sound(self):self._meow()def _meow(self):print("喵喵叫")if __name__ == '__main__':dog = Dog()dog.make_sound()cat = Cat()cat.make_sound()

实现鸭子的行为

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from abc import ABC, abstractmethodclass FlyBehavior:def fly(self):raise NotImplementedErrorclass FlyWithWings(FlyBehavior):def fly(self):print("鸭子飞行")class FlyNoWay(FlyBehavior):def fly(self):print('不会飞')class QuackBehavior(ABC):@abstractmethoddef quack(self):passclass Quack(QuackBehavior):def quack(self):print('鸭子呱呱叫')class Squeak(QuackBehavior):def quack(self):print('橡皮鸭子呱呱叫')class MuteQuack(QuackBehavior):def quack(self):print('不会叫')

鸭子类

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class Duck:def __init__(self):self.fly_behavior = Noneself.quack_behavior = Nonedef perform_fly(self):if self.fly_behavior:self.fly_behavior.fly()def perform_quack(self):if self.quack_behavior:self.quack_behavior.quack()def swim(self):pass@abstractmethoddef display(self):pass

整合鸭子的行为

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class MallardDuck(Duck):def __init__(self):super().__init__()self.fly_behavior = FlyWithWings()self.quack_behavior = Quack()def display(self):print("I'm a real Mallard Duck")

测试Duck

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if __name__ == '__main__':mallard = MallardDuck()mallard.perform_quack()mallard.perform_fly()

动态设定行为

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class Duck:...def set_fly_behavior(self, fly_behavior: FlyBehavior):self.fly_behavior = fly_behaviordef set_quack_behavior(self, quack_behavior: QuackBehavior):self.quack_behavior = quack_behaviorclass ModelDuck(Duck):def __init__(self):super().__init__()self.fly_behavior = FlyNoWay()self.quack_behavior = Quack()def display(self):print("I'm a model duck")class FlyRocketPowered(FlyBehavior):"""利用火箭动力的飞行行为"""def fly(self):print("I'm flying with a rocket!")if __name__ == '__main__':model = ModelDuck()model.perform_fly()model.set_fly_behavior(FlyRocketPowered())model.perform_fly()

或者换一种方式设置属性，效果一样


class Duck:def __init__(self):self._fly_behavior = Noneself._quack_behavior = None...@propertydef fly_behavior(self):return self._fly_behavior@fly_behavior.setterdef fly_behavior(self, fly_behavior: FlyBehavior):self._fly_behavior = fly_behavior@propertydef quack_behavior(self):return self._quack_behavior@quack_behavior.setterdef quack_behavior(self, quack_behavior: QuackBehavior):self._quack_behavior = quack_behaviorif __name__ == '__main__':model = ModelDuck()model.perform_fly()model.fly_behavior = FlyRocketPowered()# model.set_fly_behavior(FlyRocketPowered())model.perform_fly()

完整代码


from abc import ABC, abstractmethod
from typing import Optionalclass FlyBehavior:"""飞行行为"""def fly(self):raise NotImplementedErrorclass FlyWithWings(FlyBehavior):"""用翅膀飞行"""def fly(self):print("I'm flying!!")class FlyNoWay(FlyBehavior):"""不支持飞行"""def fly(self):print("I can't fly")class QuackBehavior(ABC):"""发出声音行为"""@abstractmethoddef quack(self):passclass Quack(QuackBehavior):def quack(self):print('鸭子呱呱叫')class Squeak(QuackBehavior):def quack(self):print('橡皮鸭子呱呱叫')class MuteQuack(QuackBehavior):def quack(self):print('不会叫')class Duck:def __init__(self,fly_behavior: Optional[FlyBehavior] = None,quack_behavior: Optional[QuackBehavior] = None):self._fly_behavior = fly_behaviorself._quack_behavior = quack_behaviordef perform_fly(self):if self.fly_behavior:self.fly_behavior.fly()def perform_quack(self):if self.quack_behavior:self.quack_behavior.quack()def swim(self):pass@abstractmethoddef display(self):pass# def set_fly_behavior(self, fly_behavior: FlyBehavior):#     self.fly_behavior = fly_behavior## def set_quack_behavior(self, quack_behavior: QuackBehavior):#     self.quack_behavior = quack_behavior@propertydef fly_behavior(self):return self._fly_behavior@fly_behavior.setterdef fly_behavior(self, fly_behavior: FlyBehavior):self._fly_behavior = fly_behavior@propertydef quack_behavior(self):return self._quack_behavior@quack_behavior.setterdef quack_behavior(self, quack_behavior: QuackBehavior):self._quack_behavior = quack_behaviorclass MallardDuck(Duck): # 继承，属于鸭子 IS-A，是一种鸭子的子类型def __init__(self):super().__init__()self.fly_behavior = FlyWithWings() # 组合，拥有飞行行为 HAS-Aself.quack_behavior = Quack() # 组合，拥有发出声音行为 HAS-Adef display(self):print("I'm a real Mallard Duck")class ModelDuck(Duck):def __init__(self):super().__init__()self.fly_behavior = FlyNoWay()self.quack_behavior = Quack()def display(self):print("I'm a model duck")class FlyRocketPowered(FlyBehavior):"""利用火箭动力的飞行行为"""def fly(self):print("I'm flying with a rocket!")if __name__ == '__main__':mallard = MallardDuck()mallard.perform_quack()mallard.perform_fly()model = ModelDuck()model.perform_fly()model.fly_behavior = FlyRocketPowered()# model.set_fly_behavior(FlyRocketPowered())model.perform_fly()

总结

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练习题

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from abc import abstractmethodclass WeaponBehavior:"""武器行为"""@abstractmethoddef use_weapon(self):"""使用武器"""passclass KnifeBehavior(WeaponBehavior):def use_weapon(self):return '匕首'class BowAndArrowBehavior(WeaponBehavior):def use_weapon(self):return '弓箭'class AxeBehavior(WeaponBehavior):def use_weapon(self):return '斧头'class SwordBehavior(WeaponBehavior):def use_weapon(self):return '宝剑'class Character:"""人物"""def __init__(self, w: WeaponBehavior = None):self._weapon = w@propertydef weapon(self):return self._weapon@weapon.setterdef weapon(self, w: WeaponBehavior):self._weapon = wdef fight(self):"""战斗"""if self._weapon is None:print(f"{self.__class__.__name__} has no weapon!")returnweapon = self._weapon.use_weapon()print(f"{self.__class__.__name__} use {weapon} fight")@abstractmethoddef display(self) -> None:passclass Queen(Character):def display(self) -> None:print("I'm a Queen")class King(Character):def display(self) -> None:print("I'm a King")class Troll(Character):def display(self) -> None:print("I'm a Troll")class Knight(Character):def display(self) -> None:print("I'm a Knight")if __name__ == '__main__':queen = Queen()queen.fight()queen.weapon = KnifeBehavior()queen.fight()king = King(KnifeBehavior())king.fight()king.weapon = BowAndArrowBehavior()king.fight()