DateTime('2009/06/16') != DateTime('2009-06-16')

Be careful when parsing dates with the Zope DateTime module.

Recently I have been bitten by a small difference in the way the DateTime module parses differently formatted date strings. Naively, you would think there is not difference:

>>> from DateTime import DateTime
>>> DateTime('2009/06/16')
DateTime('2009/06/16')
>>> DateTime('2009-06-16')
DateTime('2009/06/16')

So far, so good. But:

>>> DateTime('2009/06/16') == DateTime('2009-06-16')
False

Wait… What?!?

>>> DateTime('2009/06/16').rfc822()
'Tue, 16 Jun 2009 00:00:00 +0200'
>>> DateTime('2009-06-16').rfc822()
'Tue, 16 Jun 2009 00:00:00 +0000'

As you can see, the way you format the date before feeding it to DateTime matters: it may take the timezone into account. And this can really mess up catalog queries if you use slashes when storing your content and dashes for the query (or the other way around). I’m sure this is documented somewhere, but why search for documentation if you ‘know’ how it works. :)