[Python-Dev] Re: dateutil

[Paul Moore]

Greg Ewing <greg at cosc.canterbury.ac.nz> writes:

> Gustavo Niemeyer <niemeyer at conectiva.com>:
>
>> (just as examples)
>> 
>> d + relativedelta(day=1)
>> d + relativedelta(day=31)
>
> Sorry, but the more I see of this usage the worse it looks. Here
> you're effectively using '+' as an assignment operator. To me, that's
> a gross abuse of the Python language.

You're right, that's a particularly nasty example. More "normal"
usages feel far better, because they do feel like additions to me. You
could improve these cases by renaming relativedelta as something like
duration_until(), but really that's only hiding the issue.

Nevertheless, I *do* like the functionality. And the conciseness.

In some ways, i'd rather spell these examples as

    d.replace(day=1)
    d.replace(day=-1)

The former works, but the latter doesn't. One problem is that negative
arguments only really make any sense for the day argument.

Hmm, thinking about it, how will relativedelta objects get used? Most
of the time, I'd be adding relativedelta "constants". So maybe using a
simple function would be better:

    dateutil.adjust(d, day=1)
    dateutil.adjust(d, day=-1)
    dateutil.adjust(d, day=1, months=+1, days=-1)

Does this look any better?

Paul
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