Getting "not supported calendar message.ics" attachment with outlook email invite from Python

Question

Trying to write a python script to send an outlook email invite. Used instructions from here: http://www.baryudin.com/blog/sending-outlook-appointments-python.html However, I keep getting a "not supported calendar message.ics" attachemnt with my email. Code is below:

    import random

    import smtplib

    import email.MIMEText
    import email.MIMEBase

    from datetime import datetime
    from email.MIMEMultipart import MIMEMultipart

    import icalendar

    from pytz import timezone

    LOCAL_TZ = timezone("US/Eastern")

    def send_appointment(subject, description):
        start_dt = LOCAL_TZ.localize(datetime(2016, 6, 3, 17, 0, 0))
        end_dt = LOCAL_TZ.localize(datetime(2016, 6, 3, 18, 0, 0))

        cal = icalendar.Calendar()
        cal.add("prodid", "-//My oncall calendar application//test.com")
        cal.add("version", "2.0")
        cal.add("method", "REQUEST")

        event = icalendar.Event()
        event.add("attendee", MY_EMAIL)
        event.add("organizer", MY_EMAIL)
        event.add("status", "confirmed")
        event.add("summary", subject)
        event.add("description", description)
        event.add("location", "my desk")
        event.add("dtstart", start_dt)
        event.add("dtend", end_dt)
        event.add("dtstamp", start_dt)
        event["uid"] = random.random()
        event.add("priority", 5)
        event.add("sequence", 1)
        event.add("created", LOCAL_TZ.localize(datetime.now()))

        alarm = icalendar.Alarm()
        alarm.add("action", "DISPLAY")
        alarm.add("description", "Reminder")
        alarm.add("TRIGGER;RELATED=START", "-PT{0}H".format(1))
        event.add_component(alarm)

        cal.add_component(event)

        msg = MIMEMultipart("alternative")
        msg["Subject"] = subject
        msg["From"] = MY_EMAIL
        msg["To"] = MY_EMAIL
        msg["Content-class"] = "urn:content-classes:calendarmessage"

        msg.attach(email.MIMEText.MIMEText(description))

        filename = "invite.ics"

        part = email.MIMEBase.MIMEBase("text", "calendar", method="REQUEST",                     name=filename)
        part.set_payload(cal.to_ical())
        email.Encoders.encode_base64(part)
        part.add_header("Content-Description", filename)
        part.add_header("Content-class", "urn:content-classes:calendarmessage")
        part.add_header("Filename", filename)
        part.add_header("Path", filename)
        msg.attach(part)

        s = smtplib.SMTP("localhost")
        s.sendmail(MY_EMAIL, MY_EMAIL, msg.as_string())
        s.quit()

    def main():
        send_appointment("test", "desc")

    if __name__=="__main__":
        main()

NOTE: I defined MY_EMAIL but just not putting it here.

The .ics file generated is below.

    BEGIN:VCALENDAR
    VERSION:2.0
    PRODID:-//My oncall calendar application//test.com
    METHOD:REQUEST
    BEGIN:VEVENT
    SUMMARY:test
    DTSTART;TZID=US/Eastern;VALUE=DATE-TIME:20160603T170000
    DTEND;TZID=US/Eastern;VALUE=DATE-TIME:20160603T180000
    DTSTAMP;VALUE=DATE-TIME:20160603T210000Z
    UID:0.669475599056
    SEQUENCE:1
    ATTENDEE:[email protected]
    CREATED;VALUE=DATE-TIME:20160603T204723Z
    DESCRIPTION:desc
    LOCATION:my desk
    ORGANIZER:[email protected]
    PRIORITY:5
    STATUS:confirmed
    BEGIN:VALARM
    ACTION:DISPLAY
    DESCRIPTION:Reminder
    TRIGGER;RELATED=START:-PT1H
    END:VALARM
    END:VEVENT
    END:VCALENDAR

EDIT: Ok figured out the problem I think. It only understands utc timezone. So if I changed the start and end datetimes to the following then the I get a proper calendar invite.

    start_dt = datetime(2016, 6, 3, 17, 0, 0, tzinfo=pytz.utc)
    end_dt = datetime(2016, 6, 3, 18, 0, 0, tzinfo=pytz.utc)

Not entirely sure why it cannot understand other time zones. Looking at the .ics file, the date time fields look like the following.

    DTSTART;VALUE=DATE-TIME:20160603T170000Z
    DTEND;VALUE=DATE-TIME:20160603T180000Z

as opposed to

    DTSTART;TZID=US/Eastern;VALUE=DATE-TIME:20160603T170000
    DTEND;TZID=US/Eastern;VALUE=DATE-TIME:20160603T180000

The question now is why it cannot handle other timezones but I guess that should be another post.

Answer 1

Ok figured out the problem I think. It only understands utc timezone. So if I changed the start and end datetimes to the following then the I get a proper calendar invite.

    start_dt = datetime(2016, 6, 3, 17, 0, 0, tzinfo=pytz.utc)
    end_dt = datetime(2016, 6, 3, 18, 0, 0, tzinfo=pytz.utc)

Not entirely sure why it cannot understand other time zones. Looking at the .ics file, the date time fields look like the following.

    DTSTART;VALUE=DATE-TIME:20160603T170000Z
    DTEND;VALUE=DATE-TIME:20160603T180000Z

as opposed to

    DTSTART;TZID=US/Eastern;VALUE=DATE-TIME:20160603T170000
    DTEND;TZID=US/Eastern;VALUE=DATE-TIME:20160603T180000