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
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