Python nonlocal Keyword

The Python nonlocal keyword is designed to indicate that a variable within a function that is inside a function, i.e., a nested function is just not local to it, implying that it is located in the outer function.

We must define a non-local parameter with nonlocal keyword if we ever need to change its value under a nested function. Otherwise, the nested function creates a local variable using that title. It is a case-sensitive keyword.

Syntax

Following is a syntax of the Python nonlocal keyword −

nonlocal

Example

Following is a basic syntax of the Python nonlocal keyword −

def function1():  
    var1 = 200  
    def function2():  
        nonlocal var1  
        var1 = 3  
        print("The value inside the inner function: ", var1)  
    function2()  
    print("The value inside the outer function: ", var1)  
  
function1()  

Output

Following is the output of the above code −

The value inside the inner function:  3
The value inside the outer function:  3

Using global and nonlocal variables

When we defined a nonlocal variable and global variable with the same name it will result an SyntaxError.

Example

Here, we have defined a global variable, global_var with Tutotialspoint and the nonlocal variable global_var with Tp which resulted an error as both the variable names are same −

global global_var = "Tutotialspoint"
def funtion1():
    def funtion2():
        nonlocal global_var
        global_var = "Tp"
        print("The value of inside function: ", global_var)
    
    funtion2()
    print("The value of outside function: ", global_var)
    
function1()

Output

Following is the output of the above code −

File "/home/cg/root/54869/main.py", line 1
    global global_var = "Tutotialspoint"
                      ^
SyntaxError: invalid syntax

Using nonlocal Keyword in Multiple Nested Functions

The nested functions are those functions, in which more than one functions are defined with a single function. The nonlocal keyword is used in a nested function to refer to a variable in the nearest enclosing scope that is not global.

The nonlocal variable allows you to modify a variable defined in an outer (but not global) function scope, enabling the nested function to access and change the value of that variable.

Example

def function():
    var1 = 'Welcome to Tutorix'
    def function1():
        var1= 'Welcome to Tutorialspoint'
        def function2():
            nonlocal var1
            print("The value of nonlocal variable:", var1)
            var1 = "Python Tutorials"
            print("The value of nonlocal variable: ", var1)
        
        function2()
    
    function1()
    print("The value of outside function: ",var1)
function()

Output

Following is the output of the above code −

The value of nonlocal variable: Welcome to Tutorialspoint
The value of nonlocal variable:  Python Tutorials
The value of outside function:  Welcome to Tutorix