(original) (raw)
Hi Jess,
I'm sorry if I'm failing to understand the use of this function from not looking closely at your code. I'm a bit dubious about the usefulness of this (I'm not sure I understand the use cases), but I'm very open to being convinced. Datetime semantics are very important in some areas -- I use them a lot.
I'm not convinced the semantics of monthdelta are obvious.
What happens when you ask for the date in "1 month's" time on the 31st Jan? What date is a month after the 31st Jan? �
Do you have a good spec (er, I mean PEP) for this describing what happens in the edge cases and what is meant by a monthdelta? The bug notes say it "deals sensibly" with these issues, but that's really not enough to understand what the function is likely to do. At the very least, a few well-chosen examples would help to illustrate the functionality much more clearly.
Cheers,
-Tennessee
On Thu, Apr 16, 2009 at 4:18 PM, Jess Austin <jess.austin@gmail.com> wrote:
hi,
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.
This patch adds a "monthdelta" class and a "monthmod" function to the
datetime module. �The monthdelta class is much like the existing
timedelta class, except that it represents months offset from a date,
rather than an exact period offset from a date. �This allows us to
easily say, e.g. "3 months from now" without worrying about the number
of days in the intervening months.
� �>>> date(2008, 1, 30) + monthdelta(1)
� �datetime.date(2008, 2, 29)
� �>>> date(2008, 1, 30) + monthdelta(2)
� �datetime.date(2008, 3, 30)
The monthmod function, named in (imperfect) analogy to divmod, allows
us to round-trip by returning the interim between two dates
represented as a (monthdelta, timedelta) tuple:
� �>>> monthmod(date(2008, 1, 14), date(2009, 4, 2))
� �(datetime.monthdelta(14), datetime.timedelta(19))
Invariant: dt + monthmod(dt, dt+td)\[0\] + monthmod(dt, dt+td)\[1\] == dt + td
These also work with datetimes! �There are more details in the
documentation included in the patch. �In addition to the C module
file, I've updated the datetime CAPI, the documentation, and tests.
I feel this would be a good addition to core python. �In my work, I've
often ended up writing annoying one-off "add-a-month" or similar
functions. �I think since months work differently than most other time
periods, a new object is justified rather than trying to shoe-horn
something like this into timedelta. �I also think that the round-trip
functionality provided by monthmod is important to ensure that
monthdeltas are "first-class" objects.
Please let me know what you think of the idea and/or its execution.
thanks,
Jess Austin
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Tennessee Leeuwenburg
http://myownhat.blogspot.com/
"Don't believe everything you think"