Nowadays there are many professional solutions to monitor your application for the errors. Some web frameworks have even build-in tools or support plugins to catch the programming exceptions and act accordingly.
Anyway, I wanted just to build a simple proof of concept how to monitor the web server error file and, when an event occurs and the file is changed, the monitoring script should send out an email. To monitor the log file I used pyinotify python module. This is an implementation on top of inotify, offering an easy interface to interact with the changes of the filesystem.