Changing Class Members in Python

In the previous fact, we have seen that Python doesn’t have the static keyword. All variables that are assigned a value in the class declaration are class variables.

We should be careful when changing the value of a class variable. If we try to change a class variable using an object, a new instance (or non-static) variable for that particular object is created and this variable shadows the class variables. Below is a Python program to demonstrate the same.

Python3

# Class for Computer Science Student
class CSStudent:
    stream = 'cse'     # Class Variable
    def __init__(self, name, roll):
        self.name = name
        self.roll = roll

# Driver program to test the functionality
# Creating objects of CSStudent class
a = CSStudent("Geek", 1)
b = CSStudent("Nerd", 2)

print ("Initially")
print ("a.stream =", a.stream )
print ("b.stream =", b.stream )

# This thing doesn't change class(static) variable
# Instead creates instance variable for the object
# 'a' that shadows class member.
a.stream = "ece"

print ("\nAfter changing a.stream")
print ("a.stream =", a.stream )
print ("b.stream =", b.stream )

Output: 

Initially
a.stream = cse
b.stream = cse

After changing a.stream
a.stream = ece
b.stream = cse

We should change class variables using class names only.

Python3

# Program to show how to make changes to the
# class variable in Python

# Class for Computer Science Student
class CSStudent:
    stream = 'cse'     # Class Variable
    def __init__(self, name, roll):
        self.name = name
        self.roll = roll

# New object for further implementation
a = CSStudent("check", 3)
print "a.stream =", a.stream

# Correct way to change the value of class variable
CSStudent.stream = "mec"
print "\nClass variable changes to mec"

# New object for further implementation
b = CSStudent("carter", 4)

print "\nValue of variable steam for each object"
print "a.stream =", a.stream
print "b.stream =", b.stream

Output: 

a.stream = cse

Class variable changes to mec

Value of variable steam for each object
a.stream = mec
b.stream = mec

If you like GeeksforGeeks and would like to contribute, you can also write an article and mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above