Generating xCal calendar in python

"xCal", is an XML format for iCalendar data.

The iCalendar data format (RFC5545) is a widely deployed interchange format for calendaring and scheduling data.

Sample xCal document

<?xml version="1.0" encoding="utf-8"?>  
<iCalendar xmlns:xCal="urn:ietf:params:xml:ns:xcal">  
    <vcalendar>
        <version>2.0</version>
        <prodid>-//Pentabarf//Schedule 1.0//EN</prodid>
        <x-wr-caldesc>FOSDEM 2016</x-wr-caldesc>
        <x-wr-calname>Schedule for events at FOSDEM 2016</x-wr-calname>
        <vevent>
            <method>PUBLISH</method>
            <uid>123e4567-e89b-12d3-a456-426655440000</uid>
            <dtstart>20160131T090000</dtstart>
            <dtend>20160131T091000</dtend>
            <duration>00:10:00:00</duration>
            <summary>Introduction to the SDR Track- Speakers, Topics, Algorithm</summary>
            <description>&lt;p&gt;The opening talk for the SDR devroom at FOSDEM 2016.&lt;/p&gt;</description>
            <class>PUBLIC</class>
            <status>CONFIRMED</status>
            <categories>Software Defined Radio</categories>
            <url>https:/fosdem.org/2016/schedule/event/sdrintro/</url>
            <location>AW1.125</location>
            <attendee>Martin Braun</attendee>
        </vevent>
    </vcalendar>
</iCalendar>  

Each event/session will be in a seperate vevent block. Each speaker/attendee of an event/session will be in an attendee block inside a vevent block.

Some important elements are:

  1. version - Has the version of the iCalendar data
  2. prodid - Contains the name of the application/generator that generated this document
  3. x-wr-caldesc - A descriptive name for this calendar
  4. x-wr-calname - A description of the calendar

The structure and keywords used in xCal are the same as those used in the iCal format. To generate the XML document, we'll be using python's ElementTree XML API that is part of the Python standard library.

We'll be using two main classes of the ElementTree API:

  1. Element - used to create a standard node. (Used for the root node)
  2. SubElement - used to create a sub element and attache the new node to a parent

Let's start with the root iCalendar node and set the required attributes.

from xml.etree.ElementTree import Element, SubElement, tostring

i_calendar_node = Element('iCalendar')  
i_calendar_node.set('xmlns:xCal', 'urn:ietf:params:xml:ns:xcal')  

Now, to add the vcalendar node to the iCalendar node.

v_calendar_node = SubElement(i_calendar_node, 'vcalendar')  

Let's add the other aspects of the calendar to the vcalendar node as separate sub nodes.

version_node = SubElement(v_calendar_node, 'version')  
version_node.text = '2.0'

prod_id_node = SubElement(v_calendar_node, 'prodid')  
prod_id_node.text = '-//fossasia//open-event//EN'

cal_desc_node = SubElement(v_calendar_node, 'x-wr-caldesc')  
cal_desc_node.text = "Calendar"

cal_name_node = SubElement(v_calendar_node, 'x-wr-calname')  
cal_name_node.text = "Schedule for sessions"  

Now, we have added information about our calendar. Now to add the actual events to the calendar. Each event would be a vevent node, a child of vcalendar node. We can loop through all our available event/sessions and add them to the calendar.

for session in sessions:  
    v_event_node = SubElement(v_calendar_node, 'vevent')

    uid_node = SubElement(v_event_node, 'uid')
    uid_node.text = str(session.id)

    dtstart_node = SubElement(v_event_node, 'dtstart')
    dtstart_node.text = session.start_time.isoformat()

    dtend_node = SubElement(v_event_node, 'dtend')
    dtend_node.text = tz.localize(session.end_time).isoformat()

    duration_node = SubElement(v_event_node, 'duration')
    duration_node.text =  "00:30"

    summary_node = SubElement(v_event_node, 'summary')
    summary_node.text = session.title

    description_node = SubElement(v_event_node, 'description')
    description_node.text = session.short_abstract

    class_node = SubElement(v_event_node, 'class')
    class_node.text = 'PUBLIC'

    status_node = SubElement(v_event_node, 'status')
    status_node.text = 'CONFIRMED'

    categories_node = SubElement(v_event_node, 'categories')
    categories_node.text = session.session_type.name

    url_node = SubElement(v_event_node, 'url')
    url_node.text = "https://some.conf/event/" + str(session.id)

    location_node = SubElement(v_event_node, 'location')
    location_node.text = session.microlocation.name

    for speaker in session.speakers:
        attendee_node = SubElement(v_event_node, 'attendee')
        attendee_node.text = speaker.name

Please note that all the timings in the XML Document must comply with ISO 8601 and must have the date+time+timezone. Example: 2007-04-05T12:30-02:00.

We're still not done yet. We now have the XML document as an Element object. But we'll be needing it as a string to either store it somewhere or display it.

The document can be converted to a string by using the ElementTree API's tostring helper method and passing the root node.

xml_as_string = tostring(i_calendar_node)  

And that's it. You now have a proper XML document representing your events.