@classmethod @staticmethod personal understanding

The official explanation

• @classmethod

A class class method to itself as the first argument, as an example of a method to Example themselves as the first argument.

语法格式:

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

The official document links

• @staticmethod

Static method does not receive an implicit first parameter.

语法格式:

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

The official document links

characteristic

Same point

• Not instantiate the class directly call

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.

difference

category	@classmethod	@staticmethod
Syntax	The at least one parameter, the first parameter is the class itself	Can be no argument

Personal understanding

• Difference between the two

1. staticmethod decorative function is a normal function, the class is not half dime nature can not be used so that a local variable class. (eg: School class school_name), etc. can not be operated.
2. classmethod decorative function into a first parameter of the class itself, and therefore operable type, including a decorative function staticmethod reference to the class.

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.