[Python-Dev] Issue5434: datetime.monthdelta

[Paul Moore]

2009/4/16 Robert Kern <robert.kern at gmail.com>:
> 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)

Yes, but given

r = relativedelta(d1, d2)

how do I determine the number of months between d1 and d2, and the
"remainder" - what monthmod gives me. From the code, r.months looks
like it works, but it's not documented, and I'm not 100% sure if it's
always computed.

The use case I'm thinking of is converting the difference between 2
dates into "3 years, 2 months, 5 days" or whatever. I've got an
application which needs to get this right for one of the dates being
29th Feb, so I *really* get to exercise the corner cases :-)

Paul