Fixes repeating events for Nextcloud imports from Outlook.com ics exports. Use calendar.ics for the original file and the fixed file will be calendar2.ics (both in the same folder as the script)

fix_outlook_com_export_for_nextcloud.py

import os
from icalendar import Calendar
import datetime

directory = os.path.dirname(__file__)
with open(os.path.join(directory, 'calendar.ics'), 'rb') as fp:
    data = fp.read()

cal = Calendar.from_ical(data)
for event in cal.walk('vevent'):
    if 'RRULE' in event:
        actual_date = event['DTSTART'].dt if type(event['DTSTART'].dt) is datetime.date else event['DTSTART'].dt.date()
        if event['RRULE']['UNTIL'][0].date() < actual_date:
            del event['RRULE']['UNTIL']


f = open(os.path.join(directory, 'calendar2.ics'), 'wb')
f.write(cal.to_ical())
f.close()