method_class_static.md

Method vs. Classmethod vs. Staticmethod

A class can have three types of methods, a general method, a class method, and a static method.

Table of Contents

• Method vs. Classmethod vs. Staticmethod
  • Table of Contents
  • Method
  • Classmethod
    • Usage 1: Modify Class Variables
    • Usage 2: Alternative Class Constructor
  • Staticmethod

Method

General methods are those instance methods where the first receive argument must be self.

class Person:
    def __init__(self, name):
        self.name = name

    def hi(self):
        print(self.name)


x = Person("Jay")
x.hi()        # Jay
Person.hi(x)  # Jay

Classmethod

Class method, on the other hand, is a method exclusive to class, so the first argument it receives is no longer self (instance itself) but cls (class itself).

But remember to add the @classmethod decorator to the class method's head so that python recognizes that the first argument is the class itself and not the instance.

Usage 1: Modify Class Variables

The first use of class method is to modify class variables.

class Person:
    count = 0

    @classmethod
    def changeCount(cls, newCount):
        cls.count = newCount


x = Person()

Person.changeCount(10)
print(Person.count)  # 10
print(x.count)       # 10

Usage 2: Alternative Class Constructor

The second use of class method is to use it as an additional class constructor, e.g. to quickly convert a string to a class without sacrificing design.

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    @classmethod
    def fromString(cls, cls_str):
        return cls(*cls_str.split("-"))


person_str1 = "Jay-24"
person1 = Person.fromString(person_str1)
print(person1.name)  # Jay 
print(person1.age)   # 24

Staticmethod

The static method is used when you will not use instance self or class cls, but the logic of the method is very relevant to class.

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    @staticmethod
    def splitPersonString(string, split_sign="-"):
        return string.split(split_sign)

    @classmethod
    def fromString(cls, cls_str):
        return cls(*cls.splitPersonString(cls_str, ","))


person_str1 = "Jay,24"
person1 = Person.fromString(person_str1)