Python中的静态方法和类方法有什么区别 何时应该使用它们

class MathUtils:
    @staticmethod
    def add(x, y):
        return x + y

    @staticmethod
    def is_positive(x):
        return x > 0

print(MathUtils.add(5, 3))  # 输出：8
print(MathUtils.is_positive(-2)) # 输出：False

class MyClass:
    count = 0

    def __init__(self):
        MyClass.count += 1

    @classmethod
    def get_instance_count(cls):
        return cls.count

    @classmethod
    def create_from_string(cls, data_string):
        # 假设 data_string 是 "name,age" 格式
        name, age = data_string.split(",")
        return cls(name, int(age)) # 这里假设类有一个接受 name 和 age 的构造函数

print(MyClass.get_instance_count()) # 输出：0

instance1 = MyClass()
instance2 = MyClass()

print(MyClass.get_instance_count()) # 输出：2

class Singleton:
    _instance = None

    def __init__(self):
        if Singleton._instance is not None:
            raise Exception("This class is a singleton!")
        else:
            Singleton._instance = self

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

# 获取单例实例
instance1 = Singleton.get_instance()
instance2 = Singleton.get_instance()

print(instance1 is instance2) # 输出：True

# 尝试创建第二个实例会报错
# instance3 = Singleton() # 会抛出异常

class Parent:
    @classmethod
    def factory(cls):
        return cls()

class Child(Parent):
    pass

parent_instance = Parent.factory()
child_instance = Child.factory()

print(type(parent_instance)) # 输出：<class '__main__.Parent'>
print(type(child_instance))  # 输出：<class '__main__.Child'>