When you upgrade a Python module to fix a security vulnerability, you need to restart the Python processes that loaded it. So needrestart supports scanning all processes on the system to see if they are Python processes and if they loaded the Python modules that were upgraded. Same goes for Ruby and Perl, microcode and more.

The alternative approach is to just reboot after every upgrade like on Windows. That can be disruptive in some situations so needrestart was created to only restart the things that need restarting.