jayvdb added a comment. There is also the very useful https://labix.org/python-dateutil If we want our own implementation, the core problem is getting the number of days in the month, and there are a few ways to achieve that in python http://stackoverflow.com/questions/42950/get-last-day-of-the-month-in-python Once that algorithm is in core, the ability to do month operations is simple. TASK DETAIL https://phabricator.wikimedia.org/T73124 REPLY HANDLER ACTIONS Reply to comment or attach files, or !close, !claim, !unsubscribe or !assign <username>. To: jayvdb Cc: pywikipedia-bugs, Legoktm, jayvdb, XZise, Multichill, Xqt