Execute Python script from Php

I have a PHP webpage on my raspberry pi with 2 buttons (on and off) The on button button redirects to On.php The off button redirects to Off.php In "/usr/lib/cgi-bin" I have a python script that I would like to execute (script.py) I can perfectly execute it from the terminal by typing

cd /usr/lib/cgi-bin
sudo python script.py

It works if I do it from the terminal.

The problem is the PHP file (On.php) in my "/var/www" folder. This is what I wrote:

<?php
exec('cd /usr/lib/cgi-bin');
exec('sudo python script.py');
?>

Why is the script executing from the terminal, but not from my PHP?

via Chebli Mohamed