从PHP脚本调用python脚本

I have written a python script (mail.py) to send email in python, and I have written another file to submit action. I need that the file mail.py should run in background. when I am writing the follwing code

$result=shell_exec('python mail.py&');
                echo $result;

then there is no response but when i am running the file python mail.py & then it is running successfully

You must set full path to python's interpreter like:

 shell_exec('/usr/bin/python mail.py &');