Changing Class Members in Python

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

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

filter_none

edit
close

play_arrow

link
brightness_4
code

# 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

chevron_right


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 name only.

filter_none

edit
close

play_arrow

link
brightness_4
code

# 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.tream =", 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

chevron_right


Output:

a.tream = cse

Class variable changes to mec

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

This article is contributed by Nikhil Kumar Singh. If you like GeeksforGeeks and would like to contribute, you can also write an article and mail your article to contribute@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



My Personal Notes arrow_drop_up


Article Tags :

8


Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.