Python dateutils print recurrence rule according to iCalendar format (see RFC 5545)

Question

I am trying to print a recurrence rule as a string specified by iCalendar format (see RFC 5545). Im using python dateutils, in particular dateutil.rrule to create the recurr

Answer 1

Although this is written four years after the question was asked, dateutil by now has a __str__ method (see source code) which allows one to print its objects in such a form:

In [1]: from dateutil.rrule import *

In [2]: my_rrule = rrule(DAILY, count=5)

In [3]: print(my_rrule)
DTSTART:20161202T184513
FREQ=DAILY;COUNT=5

Answer 2

Here's a subclass of rrule that incorporates two suggested python-dateutil patches which enables rrule output. Beware that there might be good reasons that the patches have not been accepted, and I have only tested this for the simplest cases. Line folding is not handled.

See the bug tracker for discussion: https://bugs.launchpad.net/dateutil/+bug/943512
https://bugs.launchpad.net/dateutil/+bug/943509

FREQNAMES = ['YEARLY', 'MONTHLY', 'WEEKLY', 'DAILY', 'HOURLY', 'MINUTELY', 'SECONDLY']


class ConvertibleRRule(rrule.rrule):
    # Subclass of the `rrule class that provides a sensible __str__()
    # method, outputting ical formatted rrules.
    # Combined from the patches in these dateutil issues:
    #  https://bugs.launchpad.net/dateutil/+bug/943512
    #  https://bugs.launchpad.net/dateutil/+bug/943509
    _bysecond_internal = False
    _byminute_internal = False
    _byhour = False
    _bymonth_internal = False
    _bymonthday_internal = False
    _byweekday_internal = False

    def __init__(self, freq, dtstart=None,
                 interval=1, wkst=None, count=None, until=None, bysetpos=None,
                 bymonth=None, bymonthday=None, byyearday=None, byeaster=None,
                 byweekno=None, byweekday=None,
                 byhour=None, byminute=None, bysecond=None,
                 cache=False):
        super(ConvertibleRRule, self).__init__(
            freq, dtstart=dtstart,
            interval=interval, wkst=wkst, count=count, until=until, bysetpos=bysetpos,
            bymonth=bymonth, bymonthday=bymonthday, byyearday=byyearday, byeaster=byeaster,
            byweekno=byweekno, byweekday=byweekday,
            byhour=byhour, byminute=byminute, bysecond=bysecond,
            cache=cache)

        if (byweekno is None and byyearday is None and bymonthday is None and
                    byweekday is None and byeaster is None):
            if freq == rrule.YEARLY:
                if not bymonth:
                    self._bymonth_internal = True
                self._bymonthday_internal = True
            elif freq == rrule.MONTHLY:
                self._bymonthday_internal = True
            elif freq == rrule.WEEKLY:
                self._byweekday_internal = True

        # byhour
        if byhour is None:
            if freq < rrule.HOURLY:
                self._byhour_internal = True

        # byminute
        if byminute is None:
            if freq < rrule.MINUTELY:
                self._byminute_internal = True

        # bysecond
        if bysecond is None:
            if freq < rrule.SECONDLY:
                self._bysecond_internal = True

    freq = property(lambda s: s._freq)
    dtstart = property(lambda s: s._dtstart)
    interval = property(lambda s: s._interval)

    @property
    def wkst(self):
        if self._wkst == rrule.calendar.firstweekday():
            return None
        return rrule.weekday(self._wkst)

    count = property(lambda s: s._count)
    until = property(lambda s: s._until)
    bysetpos = property(lambda s: s._bysetpos)

    @property
    def bymonth(self):
        if self._bymonth_internal:
            return None
        return self._bymonth

    @property
    def bymonthday(self):
        if self._bymonthday_internal:
            return None
        return self._bymonthday + self._bynmonthday

    byyearday = property(lambda s: s._byyearday)
    byeaster = property(lambda s: s._byeaster)
    byweekno = property(lambda s: s._byweekno)

    @property
    def byweekday(self):
        if self._byweekday_internal:
            return None
        bynweekday, byweekday = (), ()
        if self._bynweekday:
            bynweekday = tuple(rrule.weekday(d, n) for d, n in self._bynweekday)
        if self._byweekday:
            byweekday = tuple(rrule.weekday(d) for d in self._byweekday)
        return bynweekday + byweekday

    @property
    def byhour(self):
        if self._byhour_internal:
            return None
        return self._byhour

    @property
    def byminute(self):
        if self._byminute_internal:
            return None
        return self._byminute

    @property
    def bysecond(self):
        if self._bysecond_internal:
            return None
        return self._bysecond

    def __str__(self):
        parts = ['FREQ=' + FREQNAMES[self.freq]]

        if self.interval != 1:
            parts.append('INTERVAL=' + str(self.interval))
        if self.wkst:
            parts.append('WKST=' + str(self.wkst))
        if self.count:
            parts.append('COUNT=' + str(self.count))

        for name, value in [
            ('BYSETPOS', self.bysetpos),
            ('BYMONTH', self.bymonth),
            ('BYMONTHDAY', self.bymonthday),
            ('BYYEARDAY', self.byyearday),
            ('BYWEEKNO', self.byweekno),
            ('BYWEEKDAY', self.byweekday),
            ('BYHOUR', self.byhour),
            ('BYMINUTE', self.byminute),
            ('BYSECOND', self.bysecond),
        ]:
            if value:
                parts.append(name + '=' + ','.join(str(v) for v in value))

        return ';'.join(parts)

Answer 3

There is no method or function in the python-dateutil package to do this. See this bug for a patch that may help: https://bugs.launchpad.net/dateutil/+bug/943512.