ICal has some complexity to it: Events, TODOs, Journal entries and Alarms can be repeated, removed from the feed and edited later on. This tool takes care of these complexities.
Please have a look here:
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Python library to calculate recurrence times of events, todos, alarms and journals based on icalendar RFC5545
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Python library to calculate recurrence times of events, todos, alarms and journals based on icalendar RFC5545