What is the difference between global and local variables?

A global variable can be accessed anywhere in code. A local variable can only be used in a specific code block.

Related course: Complete Python Programming Course & Exercises

global variable example

We say the scope is global, it can be used in any function or location throughout the code.

In the example below we define a global variable, y amount lines of code later we can still use that variable.

x = 3
200 lines of code

Note: In Python a global variable is always limited to the module. Thus, there is no global variable as there is in other programming languages. It’s always within a module.

python global variables scope

local variables

This is contrary to a local variable, which can only be accessed in the local scope.
In the example below, x is a local variable..

def f(x):
.. x can only be used here

If a variable is declared inside a function or loop, it’s a local variable. Global variables are usually defined at the top of the code.

best practice

Global variables are considered a bad practice because functions can have non-obvious behavior. Usually you want to keep functions small, staying within the size of the screen. If variables are declared everywhere throughout the code, it becomes less obvious to what the function does.

If you are a Python beginner, then I highly recommend this book.

Download exercises