[Tutor] Date comparison across time zones

[Martin Walsh]

frenc1z 1z wrote:
> Hello,
> I would like to compare some dates (date+time really). The dates all
> have the following RFC2822 format:
>  
> Eg. is d1 < d2?
> d1 = "Tue, 13 Jan 2009 03:27:29 -0800"
> d2 = "Tue, 13 Jan 2009 02:40:00 -0600"
>  
> My thinking is that I first need to make these two dates comparable, and
> eliminate the impact of time zone and dst. Understand that I can acheive
> this using strptime.
>  
> Been trying to parse these dates as follows: print
> datetime.strptime("Tue, 13 Jan 2009 02:40:00 -0800", "%a, %d %b %Y
> %H:%M:%S %z").
>  
> I get the following error on the conversion "ValueError: 'z' is a bad
> directive in format '%a, %d %b %Y %H:%M:%S %z'".
>  

I'm not sure how one would accomplish this with only the stdlib, but
there are at least two 3rd party modules which you may find useful.

dateutil: http://labix.org/python-dateutil
mx.DateTime: http://www.egenix.com/products/python/mxBase/mxDateTime/

Each of these implement a timezone aware date-string parser, here is an
(untested) example or two:

d1 = "Tue, 13 Jan 2009 03:27:29 -0800"
d2 = "Tue, 13 Jan 2009 02:40:00 -0600"

from dateutil import parser
dparser = parser.parser()

p1 = dparser.parse(d1)
p2 = dparser.parse(d2)

print p1 < p2

from mx.DateTime import DateTimeFrom

m1 = DateTimeFrom(d1)
m2 = DateTimeFrom(d2)

print m1 < m2

HTH,
Marty