[PYTHON] Use instance method and class method properly

Use instance method and class method properly

This time, I will write about how to use instance methods and class methods properly.

Instance method

Use when you want to control the behavior for each instance

• Cannot be called without instantiating
• Can be called by instance name.method name
• Use self as the first argument

Class method

Used to control common behavior throughout the class

• Methods can be called without instantiation
• Can be called by class name.method name
• Define by adding @ classmethod at the top of the method
• Use cls as the first argument of the class method

How to use instance method and class method in school as an example

school

class Class:
    #Number of students enrolled in the entire school
    all_students_count = 0

    def __init__(self, teacher_name, grade, group):
        self.teachername = teacher_name
        self.grade = grade
        self.group = group
        self.roster=[]

    def enter(self, name):
        #Instance method
        self.roster.append(name)
        Class.all_students_count +=1

    @classmethod
    def reset_students_count(cls, reset):
        #Class method
        cls.all_students_count = reset

#Record enrollment in 2nd grade and 3rd class with instance method
cl_23 = Class("Yamanaka", 2, 3)
cl_23.enter("Hirasawa")
cl_23.enter("Akiyama")
cl_23.enter("Tainaka")
cl_23.enter("Kotobuki")
cl_23.enter("Manabe")

print("List of enrollees in 2nd grade and 3rd class" , cl_23.roster)
print(cl_23.all_students_count)
#output:List of enrollees in 2nd grade and 3rd class['Hirasawa', 'Akiyama', 'Tainaka', 'Kotobuki', 'Manabe'], 5

#Record one set of enrollees per year with instance method
cl_11 = Class("Toyota", 1, 1)
cl_11.enter("Kaneko")
cl_11.enter("Sato")
cl_11.enter("Shimizu")

print("List of enrollees per year" , cl_11.roster)
print(cl_11.all_students_count)
#output:List of enrollees per year['Kaneko', 'Sato', 'Shimizu'], 8

#Reset all enrollments with class method
Class.reset_students_count(0)
print(cl_11.all_students_count)
#output:0