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nonlocal keyword with example in Python

Python nonlocal keyword: Here, we are going to learn about the nonlocal keyword with example.
Submitted by IncludeHelp, on April 15, 2019

Python nonlocal keyword

nonlocal is a keyword (case-sensitive) in python, it is used when we work with the nested functions and we need to use a function which is declared in outer function, if we do the same, a variable will be created as local and we then we will not be able to work with a variable in inner function which is declared in outer function.

In such a case, we can define the variable (which is declared in outer function) as a nonlocal variable in inner function using nonlocal keyword.

Syntax of nonlocal keyword

    nonlocal variable_name

Example:

def outerfunc():
    a = 10    
    def innerfunc():
        # nonlocal binding
        nonlocal a
        a = 100
            
    # calling inner function
    innerfunc()
    # printing the value of a
    print("a : ", a)

    Output:
    a : 100

Python examples of nonlocal keyword

Example 1: Define two variables in outer function and make one variable as nonlocal in inner function.

# python code to demonstrate an example 
# of nonlocal keyword 

# nested functions
def outerfunc():
    a = 10
    b = 20
    
    def innerfunc():
        # nonlocal binding
        nonlocal a
        a = 100 # will update
        b = 200 # will not update, 
                # it will be considered as a local variable
    
    # calling inner function
    innerfunc()
    # printing the value of a and b
    print("a : ", a)
    print("b : ", b)
    
# main code
# calling the function i.e. outerfunc()
outerfunc()

Output

a :  100
b :  20

As you see in the output, a and b are the variables of outerfunc() and in the innerfunc() we are binding variable a as local, thus a will not be local here but, b will be considered as local variable for innerfunc() and if we change the value of b that will be considered a new assigned for local variable(for innerfunc()) b.