Parsing ISO date/time strings - where did the parser go?

[John Nagle]

On 9/6/2012 12:51 PM, Paul Rubin wrote:
> John Nagle <nagle at animats.com> writes:
>> There's an iso8601 module on PyPi, but it's abandoned; it hasn't been
>> updated since 2007 and has many outstanding issues.
> 
> Hmm, I have some code that uses ISO date/time strings and just checked
> to see how I did it, and it looks like it uses iso8601-0.1.4-py2.6.egg .
> I don't remember downloading that module (I must have done it and
> forgotten).  I'm not sure what its outstanding issues are, as it works
> ok in the limited way I use it.
> 
> I agree that this functionality ought to be in the stdlib.

   Yes, it should.  There's no shortage of implementations.
PyPi has four.  Each has some defect.

   PyPi offers:

	iso8601 0.1.4 		Simple module to parse ISO 8601 dates
	iso8601.py 0.1dev 	Parse utilities for iso8601 encoding.
	iso8601plus 0.1.6 	Simple module to parse ISO 8601 dates
	zc.iso8601 0.2.0 	ISO 8601 utility functions

Unlike CPAN, PyPi has no quality control.

Looking at the first one, it's in Google Code.

http://code.google.com/p/pyiso8601/source/browse/trunk/iso8601/iso8601.py

The first bug is at line 67.  For a timestamp with a "Z"
at the end, the offset should always be zero, regardless of the default
timezone.  See "http://en.wikipedia.org/wiki/ISO_8601".
The code uses the default time zone in that case, which is wrong.
So don't call that code with your local time zone as the default;
it will return bad times.

Looking at the second one, it's on github:

https://github.com/accellion/iso8601.py/blob/master/iso8601.py

Giant regular expressions!  The code to handle the offset
is present, but it doesn't make the datetime object a
timezone-aware object.  It returns a naive object in UTC.

The third one is at

https://github.com/jimklo/pyiso8601plus

This is a fork of the first one, because the first one is abandonware.
The bug in the first one, mentioned above, isn't fixed.  However, if
a time zone is present, it does return an "aware" datetime object.

The fourth one is the Zope version.  This brings in the pytz
module, which brings in the Olsen database of named time zones and
their historical conversion data. None of that information is
used, or necessary, to parse ISO dates and times.  Somebody
just wanted the pytz.fixedOffset() function, which does something
datetime already does.

(For all the people who keep saying "use strptime", that doesn't
handle time zone offsets at all.)

					John Nagle