Python内置函数(11)——classmethod
英文文档:
classmethod
(function)
Return a class method for function.
A class method receives the class as implicit first argument, just like an instance method receives the instance. To declare a class method, use this idiom:
class C:
@classmethod
def f(cls, arg1, arg2, ...): ...
The @classmethod
form is a function decorator – see the description of function definitions in Function definitions for details.
It can be called either on the class (such as C.f()
) or on an instance (such as C().f()
). The instance is ignored except for its class. If a class method is called for a derived class, the derived class object is passed as the implied first argument.
Class methods are different than C++ or Java static methods. If you want those, see staticmethod()
in this section.
说明:
1. classmethod 是一个装饰器函数,用来标示一个方法为类方法
2. 类方法的第一个参数是类对象参数,在方法被调用的时候自动将类对象传入,参数名称约定为cls
3. 如果一个方法被标示为类方法,则该方法可被类对象调用(如 C.f()),也可以被类的实例对象调用(如 C().f())
>>> class C: @classmethod def f(cls,arg1): print(cls) print(arg1) >>> C.f('类对象调用类方法') <class '__main__.C'> 类对象调用类方法 >>> c = C() >>> c.f('类实例对象调用类方法') <class '__main__.C'> 类实例对象调用类方法
4. 类被继承后,子类也可以调用父类的类方法,但是第一个参数传入的是子类的类对象
>>> class D(C): pass >>> D.f("子类的类对象调用父类的类方法") <class '__main__.D'> 子类的类对象调用父类的类方法