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About the Python CalDAV Client Library

Project home

The project currently lives on github, https://github.com/python-caldav/caldav - if you have problems using the library (including problems understanding the documentation), please feel free to report it on the issue tracker there or send email to caldav@plann.no.

Objective and scope

The python caldav library should make interactions with calendar servers simple and easy. Simple operations (like find a list of all calendars owned, inserting a new event into a calendar, do a simple date search, etc) should be trivial to accomplish even if the end-user of the library has no or very little knowledge of the caldav, webdav or icalendar standards. The library should be agile enough to allow "power users" to do more advanced stuff.

The library aims to take a pragmatic approach towards compatibility - it should work as well as possible for as many as possible. This also means the library will modify icalendar data to get around known compatibility issues - so no guarantee is given on the immutability of icalendar data.

Backward compatibility support

If you stumble upon problems and cannot easily resolve them, feel free to get in touch, i.e. by the issue tracker.

The 1.x version series is not maintained anymore.

If serious problems are found with v2.2.6 during 2026, v2.2.7 will be released.

The 3.x version series (released 2026-03) is almost backwards-compatible with version 2.x. Python 3.10+ is required (Python 3.8 and 3.9 are no longer supported). The caldav/objects.py backward-compatibility shim has been removed; any code doing from caldav.objects import <something> must be updated to import directly from caldav. The wildcard import has also been removed, so if you were doing weird imports from caldav, things may break.

API deprecated with a warning in 2.x may be removed in a future 4.0 release. API deprecated without a warning in 2.x will get a deprecation warning in 4.0.

If you have any suggestions on API-changes, please comment on #92

Python compatibility notice

Most of the code is regularly tested towards different versions of Python, the oldest being Python 3.10 (as of v3.0).

Support for Python2 was officially not supported starting from caldav version 1.0.

RFC 4791, 2518, 5545, 6638 et al

RFC 4791 (CalDAV) outlines the standard way of communicating with a calendar server. RFC 4791 is an extension of RFC 4918 (WebDAV). The scope of this library is basically to cover RFC 4791/RFC 4918, the actual communication with the caldav server. (The WebDAV standard also has quite some extensions, this library supports some of the relevant extensions as well).

There exists another library webdavclient3 for handling RFC 4918 (WebDAV), ideally we should be depending on it rather than overlap it.

RFC 6638/RFC 6047 is extending the CalDAV and iCalendar protocols for scheduling purposes, work is in progress to support RFC 6638. Support for RFC 6047 is considered mostly outside the scope of this library, though for convenience this library may contain methods like accept() on a calendar invite (which involves fetching the invite from the server, editing the calendar data and putting it to the server).

This library should make it trivial to fetch an event, modify the data and save it back to the server - but to do that it's also needed to support RFC 5545 (icalendar). It's outside the scope of this library to implement logic for parsing and modifying RFC 5545, instead we depend on another library for that.

RFC 5545 describes the icalendar format. Constructing or parsing icalendar data was considered out of the scope of this library, but we do make exceptions - like, there is a method to complete a task - it involves editing the icalendar data, and now the add_event, add_todo and add_journal methods are able to construct icalendar data if needed.

There exists two libraries supporting RFC 5545, vobject and icalendar. vobject was unmaintained for several years, but seems to be actively maintained now. The caldav library originally came with vobject support, but as many people requested the vobject dependency to be replaced with icalendar, both are now supported, and the icalendar library is now consistently used internally

Misbehaving server implementations

Some server implementations may have some "caldav"-support that either doesn't implement all of RFC 4791, breaks the standard a bit, or has extra features. As long as it doesn't add too much complexity to the code, hacks and workarounds for "badly behaving caldav servers" are considered to be within the scope. Ideally, users of the caldav library should be able to download all the data from one calendar server or cloud provider, upload it to another server type or cloud provider, and continue using the library without noticing any differences. To get there, it may be needed to add tweaks in the library covering the things the servers are doing wrong.

There exists an extension to the standard covering calendar color and calendar order, allegedly with an xml namespace http://apple.com/ns/ical/. That URL gives (301 https and then) 404. I've so far found no documentation at all on this extension - however, it seems to be supported by several caldav libraries, clients and servers. As of 0.7, calendar colors and order is available for "power users".

Notable classes and workflow

For convenience, the classes above are also available as :class:`caldav.DAVClient`, :class:`caldav.Principal`, :class:`caldav.Calendar`, :class:`caldav.Event`, :class:`caldav.Todo` etc.

Compatibility

CalDAV server implementations vary widely in which optional RFC features they support, and how gracefully they handle things they do not support. The caldav library contains a compatibility layer that works around known issues automatically when the server is identified.

Compatibility hints system

..todo:: the sections about the compatibility hints should be moved somewhere else, maybe to a new document.

Server quirks and workarounds are encoded in caldav/compatibility_hints.py. Each feature has a support level:

  • full — works (as expected or better than expected)
  • quirk — supported, but needs special client-side handling
  • fragile — sometimes works, sometimes not
  • broken — server does something unexpected
  • ungraceful — server raises an HTTP error instead of handling gracefully
  • unsupported — feature is absent; attempts are silently skipped or adapted
  • unknown — not yet tested

The library calls is_supported(feature) internally before issuing requests, and applies workarounds where possible (for example, injecting an explicit time range when search.unlimited-time-range is broken).

Configuring compatibility hints

The features parameter of :func:`caldav.get_davclient` (or :class:`caldav.DAVClient`) selects a named server profile from compatibility_hints.py, or accepts a dict of feature overrides:

# Use a named profile — workarounds are applied automatically
client = get_davclient(url="https://caldav.icloud.com/", features="icloud", ...)

# Override individual features
client = get_davclient(url="https://...", features={"search.text": {"support": "unsupported"}}, ...)

(Best practice is to keep the configuration including passwords in a configuration file rather than hard-coding it in the python code)

For well-known providers (iCloud, ecloud, etc.) the features string also encodes the well-known CalDAV URL, so only the credentials are required. See :doc:`configfile` for how to specify features in the config file.

The test suite is regularly run against several calendar servers, see #45 for the latest updates. See compatibility_hints.py for the authoritative and up-to-date list of known quirks. Earlier versions of the library often had test failures that indicated the library itself was wrong; nowadays failures more often indicate that the server deviates from the standard.

Server-specific highlights

  • iCloud, Google, Zimbra are notoriously incomplete in their CalDAV support — see the server profile names icloud, google, zimbra in compatibility_hints.py for the current list of known issues.

    iCloud has not been tested for a while. As the maintainer has no account there, YOUR help is needed to ensure iCloud-compatibility.

    Notable iCloud limitations (tracked in #3):

    • No support for freebusy, tasks, or journals.
    • Broken or absent support for recurring events.
    • Objects deleted from one client may reappear after recreating a calendar with the same name.
    • get_object_by_uid() does not work despite following the RFC example.

    Google's CalDAV adapter does not support creating calendars; use the Google API directly for that. As with iCloud, Google support hasn't been tested for quite a while.

  • Radicale will auto-create a calendar when accessing a URL that does not exist, and listing calendars owned by the user may fail.

  • Baikal does not support date-range searches for todo tasks.

  • DAViCal has slightly broken support for date-range searches on todos.

  • OX App Suite applies a "sliding window" to all calendar REPORT queries: objects whose date lies too far in the past (or future) are invisible. There is no CalDAV mechanism to enumerate those objects — they are invisible to calendar.search(), calendar.events(), calendar.get_objects_by_sync_token(), and calendar.get_object_by_uid(); the only way to access them is a direct GET if the URL is already known. The library works around this by injecting an explicit 1970–2126 time range (search.unlimited-time-range: broken), which makes recurring events with future occurrences visible, but truly old non-recurring objects remain inaccessible. OX also rejects VTODOs containing RRULE with HTTP 400, and VTODOs must be stored in a calendar explicitly created for the VTODO component type.

  • Calendar creation is not mandatory under RFC 4791. Most self-hosted servers support it; Google's CalDAV adapter does not.

  • Recurring events and tasks are non-trivial to implement correctly on the server side. DAViCal and Baikal are the only servers known to handle them correctly in the test suite.

Some notes on CalDAV URLs

From v2.1, well-known URLs were hard-coded into the compatibility_hints. As of v2.2, auto-detection based on RFC 6764 is supported. This protocol is widely used. For servers supporting it, it's sufficient to add something like "demo2.nextcloud.com" in the URL. For well-known calendar providers, it's not needed to enter anything in the URL, it suffices to put i.e. features="ecloud" into the connection parameters.

CalDAV URLs can be quite confusing, some software requires the URL to the calendar, other requires the URL to the principal. The Python CalDAV library does support accessing calendars and principals using such URLs, but the recommended practice is to configure up the CalDAV root URL and tell the library to find the principal and calendars from that. Typical examples of CalDAV URLs:

  • iCloud: https://caldav.icloud.com/. Note that there is no template for finding the calendar URL and principal URL for iCloud - such URLs contains some ID numbers, by simply sticking to the recommended practice the caldav library will find those URLs. A typical icloud calendar URL looks like https://p12-caldav.icloud.com/12345/calendars/CALNAME. If you encounter troubles with iCloud, try toggling between IPv4 and IPv6 (see [issue 393](#393))
  • Google - legacy: https://www.google.com/calendar/dav/, The calendar URL for the primary personal calendar seems to be of the format https://www.google.com/calendar/dav/donald%40gmail.com/events. When creating new calendars, they seem to end up under a global namespace.
  • Google - new api: see https://developers.google.com/calendar/caldav/v2/guide. There is some information in #119 on how to connect to Google, and there are two contributed :ref:`examples:examples` on how to obtain a bearer token and use it in the caldav lbirary. There is also a blog post describing the process.
  • DAViCal: The caldav URL typically seems to be on the format https://your.server.example.com/caldav.php/, though it depends on how the web server is configured. The primary calendars have URLs like https://your.server.example.com/caldav.php/donald/calendar and other calendars have names like https://your.server.example.com/caldav.php/donald/golfing_calendar.
  • Zimbra: The caldav URL is typically on the format https://mail.example.com/dav/, calendar URLs can be on the format https://mail.example.com/dav/donald@example.com/My%20Golfing%20Calendar. Display name always matches the last part of the URL.
  • Fastmail: https://caldav.fastmail.com/dav/ - note that the trailing dash is significant (ref home-assistant/core#66599)
  • GMX: f"https://caldav.gmx.net/begenda/dav/{userid}@gmx.net/calendar"`
  • Purelymail: https://purelymail.com/webdav/
  • Posteo: https://posteo.de:8443/
  • all-inkl: https://webmail.all-inkl.com/calendars/
  • Lark: https://caldav-jp.larksuite.com - note that Lark offers a very limited read-only access through the CalDAV protocol.

Unit testing

To run the tests, install the test dependencies and use pytest:

$ pip install -e ".[test]"
$ pytest

tox should also work:

$ tox -e py

It will run some unit tests and some functional tests. You may want to add your own private servers into tests/caldav_test_servers.yaml, see tests/caldav_test_servers.yaml.example

Niquests vs Requests vs HTTPX

By default, CalDAV depends on the niquests library. Some people are not happy with that, there exists fallbacks to utilize httpx and requests. See the :doc:`http-libraries` document.

Documentation

To build the documentation, install sphinx and run:

$ python setup.py build_sphinx

Code of Conduct

While I hope we never will need to refer to it, the Contributor Covenant applies to this project, see also CODE_OF_CONDUCT. Avoid toxic negativity in general, but Tobias Brox can probably handle some blunt criticism if it may help getting the project on a better track.

License

Caldav is dual-licensed under the GNU GENERAL PUBLIC LICENSE Version 3 or the Apache License 2.0.