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The main feature of a static variable is that when it is initialized with a value, its value remains the same for all the objects of a class.

Features of a static variable

• A static variable belongs to the class in which it is defined, hence, a static variable is called a class variable.


• Only one copy of a static variable is shared by all the objects of its class.


• A static variable can be accessed by its class name with a dot operator or even by an object of its class(only when there is no instance with the same name as a static variable).

• Accessing a static variable using its class name.


A static variable can be accessed directly by using its class name and a dot operator. Let us see an example.



# Python - Direct access of a static variable using the name of its class


class Test:
    
    #Defining two class variable/static variables of class Test
    n = 10
    message = 'Have a good day!'


	
# Accessing a static variable, n,  using its class name with a dot operator
print(Test.n)

# Accessing a static variable, message, using its class name with a dot operator
print(Test.message)





Output is :




10
Have a good day!








• Accessing a static variable using the object of its class.


A static variable can be accessed directly by using the object of its class with a dot operator, but with a condition that there should be no instance variable with the same name. In this case, compiler internally replaces the object name with its class name. Let us see an example.



# Python - Direct access of a static variable using the object of its class


class Test:
    
    #Defining two class variable/static variables of class Test
    n = 10
    message = 'Have a good day!'



# Creating an object of a class 
ob = Test()


# Accessing a static variable, n,  using its class name with a dot operator
print(Test.n)


# Accessing a static variable, message, using the object of the same class with a dot operator
print(ob.message)





Output is :




10
Have a good day!






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• Accessing a static variable from within its class method.



A static variable can be accessed from within a general method of its class in two ways -:
• By using its class name.
• By using the current object of its class through the self keyword, but with a condition that we are not changing its value or it will lead to the creation of an instance variable with the same name.
Let us see an example.



# Direct access of a static variable


class Test:
    
    #Defining a class variable/static variable with an int value 10
    n = 10


    # Defining a method
    def method(self):

        # Accessing the static variable within this general method using its class name 
        print(Test.n)
		
	# Accessing the static variable from within this general method using self keyword i.e. current object.
        # In this case, an object name is internally replaced by its class name while calling a static variable
        print(self.n)
		
	
	# self.n =10 would have not modified the static variable to 10
	# but would've rather created an instance variable with the same name
		
		



        
# Calling the constructor to create an object of class
ob1 = Test()	



# Calling the method() associated with the object, ob1
ob1.method()



# Accessing the value of a static variable using the object name
print(ob1.n)



#Printing the value of static variable of the class using the class name
print(Test.n)





Output is :




10
10
10
10








• Instance variable overshadowing static variable.


An instance variable with the same as a static variable, will overshadow the static variable. In such case, accessing a static variable by using the object of its class(like in the previous example) will give us access to the instance variable and not the static variable. Let us see an example.



# Direct access of a static variable


class Test:
    
    #Defining a class variable/static variable with an int value 10 
    n = 10


    # Defining a method
    def method(self):

        # Defining an instance variable with the same name as the static variable i.e. 'n'
        self.n = Test.n + 10



        
# Calling the constructor to create an object of class
ob1 = Test()	


# Calling the method() associated with the object, ob1
ob1.method()


# Accessing an instance variable, n, has overshadowed  the static variable with the same name
# Hence, trying to access the static variable using the object name gives us instance variable.
print(ob1.n)


# Accessing the value of static variable of the class using the class name
print(Test.n)





Output is :




20
10








• Incorrect access of a static variable.


A static variable cannot be accessed directly.



class Test:
    
    #Defining a class variable/static variable with an int value 10
    n = 10


# Directly accessing the static variable will lead to an error
print(n)





Output is :




Traceback (most recent call last):
  File "D:/Python Programs/static7.py", line 7, in <module>
    print(n)
NameError: name 'n' is not defined


As you see in the last program, direct access of a static variable leads to an error, therefore, a static variable should only be accessed using its class name or with its class object(if there is no instance variable with the same name as the static variable).

In the next article, we are going to discuss static function in Python, its use and how to define it and more. So, please turn the page :-)





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