Generate iCal VTIMEZONE block with DAYLIGHT and STANDARD components, based on pytz zoneinfo data

vtz_block.py

import pytz
import icalendar
import datetime

def generate_vtimezone(timezone):
    if not timezone:  # UTC as a fallback doesn't work, since it has no transition info
        return None
    z = pytz.timezone(timezone)
    utc = pytz.timezone('utc')
    dst1, std1, dst2, std2 = filter(lambda x: x[0].year in (datetime.now().year, datetime.now().year + 1),
                                    zip(z._utc_transition_times, z._transition_info))
    vtz = icalendar.Timezone(tzid=timezone)
    dl = icalendar.TimezoneDaylight()
    utcoffset, dstoffset, tzname = dst1[1]
    offsetfrom = std1[1][0]
    dl.add('dtstart', dst1[0] + offsetfrom)
    dl.add('rdate', dst1[0] + offsetfrom)
    dl.add('rdate', dst2[0] + offsetfrom)
    dl.add('tzoffsetfrom', offsetfrom)
    dl.add('tzoffsetto', utcoffset)
    dl.add('tzname', tzname)
    vtz.add_component(dl)
    dl = icalendar.TimezoneStandard()
    utcoffset, dstoffset, tzname = std1[1]
    offsetfrom = dst1[1][0]
    dl.add('dtstart', std1[0] + offsetfrom)
    dl.add('rdate', std1[0] + offsetfrom)
    dl.add('rdate', std2[0] + offsetfrom)
    dl.add('tzoffsetfrom', offsetfrom)
    dl.add('tzoffsetto', utcoffset)
    dl.add('tzname', tzname)
    vtz.add_component(dl)
    return vtz