RFC3339: Simple, canonical date parsing and formatting for Python

This page is a mirrored copy of an article originally posted on the LShift blog; see the archive index here.

As part of a customer project some years ago, we wrote an implementation of the interesting parts of RFC 3339 for Python. The abstract for the RFC says

This document defines a date and time format for use in Internet protocols that is a profile of the ISO 8601 standard for representation of dates and times using the Gregorian calendar.

We needed to be able to robustly transfer timestamps between languages (Javascript and Python, chiefly) without getting tangled up in timezone troubles or complex ambiguous parsing problems.

Our code provides

  • simple, standard, robust, cross-language (e.g. Javascript) format for parsing and printing time stamps
  • a standard no-frills “UTC” tzinfo class and singleton instance
  • a standard no-frills fixed-offset tzinfo class
  • other utilities for helping write robust timezone-aware time manipulation code


These examples are taken from the doctests/docstrings in the module source itself. See the module documentation for many more informative examples.

Parsing a timestamp, with timezone support and timestamp equivalence:

>>> midnightUTC = parse_datetime("2008-08-24T00:00:00Z")
>>> oneamBST = parse_datetime("2008-08-24T01:00:00+01:00")
>>> midnightUTC == oneamBST

Printing a timestamp:

>>> oneamBST.isoformat()
>>> parse_datetime("2008-08-24T00:00:00.123Z").isoformat()

Downloading the code

The code is available on github. It’s MIT-licensed.

  • Browse the code here
  • Download a tarball of the latest code

You can also install the module directly from github using pip:

pip install -e git://github.com/tonyg/python-rfc3339.git#egg=rfc3339


On 20 May, 2010 at 10:20 am, jpc wrote:

Have you considered TAI64[1]?

On 21 May, 2010 at 2:45 am, tonyg wrote:

TAI64 is fine, but not supported natively by Javascript (unlike the RFC3339 profile of ISO8601). It’s also not so human readable.