In Python, how to parse a string representing a set of keyword arguments such that the order does not matter

Question

I\'m writing a class RecurringInterval which - based on the dateutil.rrule object - represents a recurring interval in time. I have defined a custom, human-read

Answer 1

You have many options here, each with different downsides.

One approach would be to use a repeated alternation, like (by weekday|by month)*:

(?PWeekly)?\s+from (?P.+?)\s+till (?P.+?)(?:\s+by weekday (?P.+?)|\s+by month (?P.+?))*$

This will match strings of the form week month and month week, but also week week or month week month etc.

Another option would be use lookaheads, like (?=.*by weekday)?(?=.*by month)?:

 (?PWeekly)?\s+from (?P.+?)\s+till (?P.+?(?=$| by))(?=.*\s+by weekday (?P.+?(?=$| by))|)(?=.*\s+by month (?P.+?(?=$| by))|)

However, this requires a known delimiter (I used " by") to know how far to match. Also, it'll silently ignore any extra characters (meaning it'll match strings of the form by weekday [some gargabe] by month).