@classmethod @staticmethod 个人理解

官方解释

• @classmethod

一个类方法把类自己作为第一个实参, 就像一个实例方法把实例自己作为第一个实参.

语法格式:

class C:
    @classmethod
    def f(cls, arg1, arg2, ...): ...

官方文档链接

• @staticmethod

静态方法不会接收隐式的第一个参数.

语法格式:

class C:
    @staticmethod
    def f(arg1, arg2, ...): ...

官方文档链接

特性

相同点

• 可不实例化类直接调用

import time

class School(object):
    school_name = "A_Tester_School"
    address = "China_Sichuan"

    def __init__(self, student_name):
        self.student_name = "a student of A_Tester_School, name is: {} ".format(student_name)

    def age(self, birthday):
        return time.localtime().tm_year - birthday

    @classmethod
    def get_school(cls):
        return cls.school_name, cls.address

    @staticmethod
    def get_address():
        return "hello world."

# 实例调用
my_school = School("Hoo")
print(my_school.age(1991))
print(my_school.get_school())
print(my_school.get_address())
print("-"*50)
# 不实例化调用
print(School.get_school())
print(School.get_address())

# 28
# ('A_Tester_School', 'China_Sichuan')
# hello world.
# --------------------------------------------------
# ('A_Tester_School', 'China_Sichuan')
# hello world.

不同点

语法格式

至少一个参数,第一个参数为类本身

可无参数

个人理解

• 二者区别

1. staticmethod装饰的函数就是一个普通的函数, 本质上与类没有半毛钱关系.所以无法使用类的局部变量(如:School类中的school_name), 无法操作类等.
2. classmethod装饰的函数第一个入参为类本身, 因此可操作类, 包括引用类的staticmethod装饰的函数.

class ChildSchool(School):
    @classmethod
    def get_student_info(cls, student_name, birthday):
        my_school = cls(student_name)  # 实例化类
        age1 = my_school.age(birthday)  # 调用实例方法
        print("school_name: {}".format(cls.school_name))  # 不实例类, 调用类局部变量
        print("address: {}".format(my_school.address))  # 实例类, 调用类局部变量. 此处my_school可换成cls
        print("age: {}".format(age1))
        print("introduction: {}".format(my_school.student_introduction))  # 调用实例属性
        print("this a error address: {}".format(cls.get_address())) # 调用类静态方法

ChildSchool.get_student_info("Hoo", 1991)

# school_name: A_Tester_School
# address: China_Sichuan
# age: 28
# introduction: a student of A_Tester_School, name is: Hoo
# this a error address: hello world.