Python dateutil.rrule is incredibly slow

Question

I'm using the python dateutil module for a calendaring application which supports repeating events. I really like the ability to parse ical rrules using the rrulestr() function. Also, using rrule.between() to get dates within a given interval is very fast.

However, as soon as I try doing any other operations (ie: list slices, before(), after(),...) everything begins to crawl. It seems like dateutil tries to calculate every date even if all I want is to get the last date with rrule.before(datetime.max).

Is there any way of avoiding these unnecessary calculations?

Answer 1

This module is completely new to me, so thanks for that!

That said, does it help if you pass cache=True into your rrule or rruleset constructors, as documented here?

Answer 2

My guess is probably not. The last date before datetime.max means you have to calculate all the recurrences up until datetime.max, and that will reasonably be a LOT of recurrences. It might be possible to add shortcuts for some of the simpler recurrences. If it is every year on the same date for example, you don't really need to compute the recurrences inbetween, for example. But if you have every third something you must, for example, and also if you have a maximum recurrences, etc. But I guess dateutil doesn't have these shortcuts. It would probably be quite complex to implement reliably.

May I ask why you need to find the last recurrence before datetime.max? It is, after all, almost eight thousand years into the future... :-)