Python使用方法重载实现访问者模式

from abc import ABC, abstractmethod  
  
# 抽象访问者  
class AnimalVisitor(ABC):  
    @abstractmethod  
    def visit_dog(self, dog: "Dog"):  
        pass  
  
    @abstractmethod  
    def visit_cat(self, cat: "Cat"):  
        pass  
  
# 抽象动物类  
class Animal(ABC):  
    def __init__(self, name: str):  
        self.name = name  
  
    @abstractmethod  
    def accept(self, visitor: AnimalVisitor):  
        pass  
  
# 具体动物类  
class Dog(Animal):  
    def accept(self, visitor):  
        visitor.visit_dog(self)  
  
class Cat(Animal):  
    def accept(self, visitor):  
        visitor.visit_cat(self)  
  
# 具体访问者：喂食访问者  
class FeedingVisitor(AnimalVisitor):  
    def visit_dog(self, dog):  
        print(f"给{dog.name}喂狗粮")  
  
    def visit_cat(self, cat):  
        print(f"给{cat.name}喂猫粮")  
  
# 具体访问者：检查健康访问者  
class HealthCheckVisitor(AnimalVisitor):  
    def visit_dog(self, dog):  
        print(f"检查{dog.name}的疫苗接种情况")  
  
    def visit_cat(self, cat):  
        print(f"检查{cat.name}是否需要洗澡")

def main():  
    # 创建动物  
    dog = Dog("旺财")  
    cat = Cat("咪咪")  
  
    # 创建访问者  
    feeding_visitor = FeedingVisitor()  
    health_visitor = HealthCheckVisitor()  
  
    # 创建动物列表  
    animals = [dog, cat]  
  
    # 执行不同的操作  
    print("=== 喂食时间 ===")  
    for animal in animals:  
        animal.accept(feeding_visitor)  
  
    print("\n=== 健康检查 ===")  
    for animal in animals:  
        animal.accept(health_visitor)
  
  
if __name__ == "__main__":  
    main()

from abc import ABC, abstractmethod  
from functools import singledispatchmethod  
  
# 抽象访问者  
class AnimalVisitor(ABC):  
    @abstractmethod  
    def visit(self, animal: "Animal"):  
        pass  
  
# 抽象动物类  
class Animal(ABC):  
    def __init__(self, name: str):  
        self.name = name  
  
    def accept(self, visitor: AnimalVisitor):  
        visitor.visit(self)  
  
# 具体动物类  
class Dog(Animal): ...  
  
class Cat(Animal): ...  
  
# 具体访问者：喂食访问者  
class FeedingVisitor(AnimalVisitor):  
    @singledispatchmethod  
    def visit(self, animal: Animal):  
        raise NotImplementedError(f"{type(animal)} 未重载 visit方法")  
  
    @visit.register(Dog)  
    def _(self, dog):  
        print(f"给{dog.name}喂狗粮")  
  
    @visit.register(Cat)  
    def _(self, cat):  
        print(f"给{cat.name}喂猫粮")  
  
# 具体访问者：检查健康访问者  
class HealthCheckVisitor(AnimalVisitor):  
  
    @singledispatchmethod  
    def visit(self, animal: Animal):  
        raise NotImplementedError(f"{type(animal)} 未重载 visit方法")  
  
    @visit.register(Dog)  
    def _(self, dog):  
        print(f"检查{dog.name}的疫苗接种情况")  
  
    @visit.register(Cat)  
    def _(self, cat):  
        print(f"检查{cat.name}是否需要洗澡")