YADTR (Yet Another DateTime Rant)

Skip Montanaro skip at pobox.com
Wed Mar 26 16:39:50 CET 2014


On Wed, Mar 26, 2014 at 10:04 AM, Roy Smith <roy at panix.com> wrote:
> No, what you said was "negative four days, positive 3605 seconds".

My apologies for not showing all my work, professor. I use datetime
and timedelta objects all the time. I did the arithmetic to go from
3605 to one hour, five minutes in my head.

The point of my post was that there is no obvious one best way to
present negative timedeltas in a human readable form. In my usage it's
not generally a big deal, as most of the time I want to display
datetime objects. In your case, it's obviously a problem. If Tim
thought that timedelta objects would be presented to users as a
regular course of doing business, maybe he would have given them a
strftime() method. I suggest you write a function to format it the way
you want and be done with it.

You might consider taking a crack at a strftime() (and strptime?)
implementation for timedelta objects that uses the ISO 8601 notation
and submit it as a patch for datetimemodule.c. Note though, that the
ISO8601 representation isn't without its own flaws (which might
explain why Tim avoided it BITD):

* It doesn't appear to provide a way to represent fractions of a
second (though perhaps all the fields can be fractional)
* How many days are in a month or a year? (It has format codes for
both. Writing a useful strptime is probably impossible.)
* It has other ambiguities ("M" represents both months and minutes -
what were they thinking?)

Skip



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