Python中staticmethod和classmethod的作用与区别

一般来说，要使用某个类的方法，需要先实例化一个对象再调用方法。

而使用@staticmethod或@classmethod，就可以不需要实例化，直接类名.方法名()来调用。

这有利于组织代码，把某些应该属于某个类的函数给放到那个类里去，同时有利于命名空间的整洁。

既然@staticmethod和@classmethod都可以直接类名.方法名()来调用，那他们有什么区别呢

从它们的使用上来看

如果在@staticmethod中要调用到这个类的一些属性方法，只能直接类名.属性名或类名.方法名。

而@classmethod因为持有cls参数，可以来调用类的属性，类的方法，实例化对象等，避免硬编码。

要明白，什么是实例方法、静态方法和类方法：

class Demo(object): def instance_method(self, your_para): """ this is an instance_method you should call it like the follow: a = Demo() a.instance_method(your_para) plus: in python, we denote 'cls' as latent para of Class while 'self' as latent para of the instance of the Class :param your_para:  :return:  """ print("call instance_method and get:", your_para) @classmethod def class_method(cls, your_para): """ this is a class_method you can call it like the follow: method1: a = Demo() a.class_method(your_para) method2: Demo.class_method plus: in python, we denote 'cls' as latent para of Class while 'self' as latent para of the instance of the Class :param your_para:  :return:  """ print("call class_method and get:", your_para) @staticmethod def static_method(your_para): """ this is a static_method and you can call it like the  methods of class_method :param your_para:  :return:  """ print("call static_method and get:", your_para)

虽然类方法在调用的时候没有显式声明cls，但实际上类本身是作为隐含参数传入的。这就像实例方法在调用的时候也没有显式声明self,但实际上实例本身是作为隐含参数传入的。

对于静态函数，我们一般把与类无关也与实例无关的函数定义为静态函数。例如入口检查的函数就最好定义成静态函数。

类方法的妙处， 在继承中的作用：

class Fruit(object): total = 0 # 这是一个类属性 @classmethod def print_total(cls): print('this is the ', cls, '.total:', cls.total, ' and its id: ', id(cls.total)) # cls是类本身，打印类属性total的值 print('this is the Fruit.total:', Fruit.total, 'and its id: ', id(Fruit.total)) print("=======================") @classmethod def set(cls, value): cls.total = valueclass Apple(Fruit): passclass Orange(Fruit): passapp1 = Apple()app1.set(10)app1.print_total()Apple.print_total()Fruit.set(2)app1.print_total()Fruit.print_total()"""output:this is the <class '__main__.Apple'> .total: 10 and its id: 1355201264this is the Fruit.total: 0 and its id: 1355200944=======================this is the <class '__main__.Apple'> .total: 10 and its id: 1355201264this is the Fruit.total: 0 and its id: 1355200944=======================this is the <class '__main__.Apple'> .total: 10 and its id: 1355201264this is the Fruit.total: 2 and its id: 1355201008=======================this is the <class '__main__.Fruit'> .total: 2 and its id: 1355201008this is the Fruit.total: 2 and its id: 1355201008======================="""