[Python-Dev] Issue5434: datetime.monthdelta

[Robert Kern]

On 2009-04-16 13:42, Paul Moore wrote:
> 2009/4/16 Ned Deily<nad at acm.org>:
>> In article
>> <b8ad139e0904152318p5473cbe5yb5f55a19894cc834 at mail.gmail.com>,
>>   Jess Austin<jess.austin at gmail.com>  wrote:
>>> I'm new to python core development, and I've been advised to write to
>>> python-dev concerning a feature/patch I've placed at
>>> http://bugs.python.org/issue5434, with Rietveld at
>>> http://codereview.appspot.com/25079.
>> Without having looked at the code, I wonder whether you've looked at
>> python-dateutil.   I believe its relativedelta type does what you
>> propose, plus much more, and it has the advantage of being widely used
>> and tested.
>
> The key thing missing (I believe) from dateutil is any equivalent of monthmod.
>
> Hmm, it might be possible via relativedelta(d1,d2), but it's not clear
> to me from the documentation precisely what attributes/methods of a
> relativedelta object are valid for getting data *out* of it.

I thought the examples were quite clear. relativedelta() has an alternate 
constructor precisely suited to these calculations but is general and handles 
more than just months.

 >>> from dateutil.relativedelta import *
 >>> dt = relativedelta(months=1)
 >>> dt
relativedelta(months=+1)
 >>> from datetime import datetime
 >>> datetime(2009, 1, 15) + dt
datetime.datetime(2009, 2, 15, 0, 0)
 >>> datetime(2009, 1, 31) + dt
datetime.datetime(2009, 2, 28, 0, 0)
 >>> dt.months
1
 >>> datetime(2009, 1, 31) + relativedelta(years=-1)
datetime.datetime(2008, 1, 31, 0, 0)

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco