详解Python中类方法@classmethod的应用技巧

class MyClass:
    @classmethod
    def my_class_method(cls, arg1, arg2):
        # 类方法的实现
        pass

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age
    
    @classmethod
    def from_birth_year(cls, name, birth_year):
        age = 2024 - birth_year
        return cls(name, age)

person = Person.from_birth_year("Alice", 1990)
print(person.name, person.age)  # 输出：Alice 34

class Shape:
    @classmethod
    def create_shape(cls, shape_type):
        if shape_type == "circle":
            return Circle()
        elif shape_type == "rectangle":
            return Rectangle()

class Circle(Shape):
    pass

class Rectangle(Shape):
    pass

circle = Shape.create_shape("circle")
rectangle = Shape.create_shape("rectangle")

class Singleton:
    _instance = None
    
    @classmethod
    def get_instance(cls):
        if cls._instance is None:
            cls._instance = cls()
        return cls._instance

singleton1 = Singleton.get_instance()
singleton2 = Singleton.get_instance()

print(singleton1 is singleton2)  # 输出：True

class MyClass:
    class_variable = "Hello, world!"

    @classmethod
    def class_method(cls):
        print("Class variable:", cls.class_variable)

    @staticmethod
    def static_method():
        print("This is a static method.")

# 调用类方法
MyClass.class_method()  # 输出：Class variable: Hello, world!

# 调用静态方法
MyClass.static_method()  # 输出：This is a static method.

class ParentClass:
    @classmethod
    def class_method(cls):
        print("Parent class method")

class ChildClass(ParentClass):
    @classmethod
    def class_method(cls):
        print("Child class method")

# 调用子类的类方法
ChildClass.class_method()  # 输出：Child class method

class MyClass:
    class_variable = "Hello, world!"

    @classmethod
    def class_method(cls):
        print("Class variable:", cls.class_variable)

    def instance_method(self):
        print("Instance method:", self.class_variable)

# 调用类方法
MyClass.class_method()  # 输出：Class variable: Hello, world!

# 创建类的实例
my_instance = MyClass()

# 调用实例方法
my_instance.instance_method()  # 输出：Instance method: Hello, world!