Class or Static Variables in Python
All objects share class or static variables. An instance or non-static variables are different for different objects (every object has a copy). For example, let a Computer Science Student be represented by class CSStudent. The class may have a static variable whose value is “cse” for all objects. And class may also have non-static members like name and roll. In C++ and Java, we can use static keywords to make a variable a class variable. The variables which don’t have a preceding static keyword are instance variables. See this for the Java example and this for the C++ example.
The Python approach is simple; it doesn’t require a static keyword.
All variables which are assigned a value in the class declaration are class variables. And variables that are assigned values inside methods are instance variables.
Python
# Python program to show that the variables with a value # assigned in class declaration, are class variables # Class for Computer Science Student class CSStudent: stream = 'cse' # Class Variable def __init__( self ,name,roll): self .name = name # Instance Variable self .roll = roll # Instance Variable # Objects of CSStudent class a = CSStudent( 'Geek' , 1 ) b = CSStudent( 'Nerd' , 2 ) print (a.stream) # prints "cse" print (b.stream) # prints "cse" print (a.name) # prints "Geek" print (b.name) # prints "Nerd" print (a.roll) # prints "1" print (b.roll) # prints "2" # Class variables can be accessed using class # name also print (CSStudent.stream) # prints "cse" # Now if we change the stream for just a it won't be changed for b a.stream = 'ece' print (a.stream) # prints 'ece' print (b.stream) # prints 'cse' # To change the stream for all instances of the class we can change it # directly from the class CSStudent.stream = 'mech' print (a.stream) # prints 'ece' print (b.stream) # prints 'mech' |
Output:
cse cse Geek Nerd 1 2 cse ece cse ece mech
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