Python Global, Local and Non-local Variables

We see the difference between global, local, and nonlocal variables of functions.

Global Variables

A Python global variable is declared outside the function or in the global scope.

This means that a global variable can be accessed inside or outside functions.

For example:

x = "global string"

def my_function():
    print("x inside:", x) # x inside: global string

my_function()
print("x outside:", x) # x outside: global string

If you want to change the value of a global variable within a function, you must use the global keyword. Otherwise, an UnboundLocalError error is raised.

x = "global string"

def my_function():
    x = x + " append something"
    print("x inside:", x)

my_function()
# UnboundLocalError: local variable 'x' referenced before assignment

Local Variables

A Python local variable is declared inside the function's body or in the local scope.

For example, a variable declared inside a function is a local variable:

def my_function():
    y = "local"
    print(y)

foo()

Output

local

Non-local Variables

Nonlocal variables are used in nested functions whose local scope is not defined.

This means that the variable can't be in either the local or global scope.

The nonlocal keyword is used to create nonlocal variables.

For example, use the nonlocal keyword to create a nonlocal variable:

def outer_function():
    x = "local"

    def inner_function():
        nonlocal x # nonlocal declaration
        x = "nonlocal"
        print("inner:", x)

    inner_function()
    print("outer:", x)


outer_function()

Output:

inner: nonlocal
outer: nonlocal

Examples

Global and Local variables in the same code

Global and local variables can be used in the same code.

If the global variable is to be modified, it must be declared within the local scope with the global keyword.

In the following example, x is a global variable and y is a local variable:

x = "global "

def foo():
    global x
    y = "local"
    x = x * 2
    print(x)
    print(y)

foo()

Global variable and Local variable with same name

The name x is used for both the global and the local variable. You get a different result when printing the same variable, because the variable is declared in both scopes (local scope inside my_function() and global scope outside my_function()).

x = 5

def my_function():
    x = 10
    print("local x:", x)

my_function()
print("global x:", x)

Output

local x: 10
global x: 5