Revision 362fbca0-fe84-436d-b9e7-93f4fd814768 - Stack Overflow

shell_exec — Execute command via shell and return the complete output as a string . [reference][1]


 <?php
 if(isset($_POST['switch'])){
 $c=escapeshellcmd("sudo python /home/pi/Desktop/test.py");
 $res=shell_exec($c);
 echo $res; // returns result to display
 }
 ?>

in your script,output is not printed that may seem to not working

 <?php
 if(isset($_POST['switch'])){
 $s=exec("sudo python /home/pi/Desktop/test.py");
 echo "$s"; 
 }
 ?>


 [1]: http://php.net/manual/en/function.shell-exec.php