[Python-Dev] datetime +/- scalars (int, long, float)?

[Guido van Rossum]

> > [Guido]
> > Then I propose to remove the feature of automatic mixing
> > int/long/float and datetime or timedelta instances in add/subtract
> > operations.  You'll have to specify what you want using a
> > timedelta(days, seconds) constructor.  That's clearer anyway.

[Kevin]
> I much prefer this.  My own datetime object uses a syntax like this:
> 
>   t = t + Delta(days=1,minutes=-5,seconds=5)

I'm considering such an extension to the timedelta() constructor too.

> > > However, lets be clear; is t=t+1 adding 1 (calendar) day or 24 hours
> > > (86400 seconds)?
> > 
> > How does it differ?  (We already ignore leap seconds.)
> 
> The concept of a "day" can be somewhat ambiguous.  I've seen
> datetime implementations that will apply DST changes when asked to
> adjust by days, but not when asked to adjust by seconds, hours or
> minutes.  So, in the general case of a DST aware datetime object,
> 
>   t + Delta(days=1) != t + Delta(hours=24)
> 
> even when ignoring leap-seconds and other micro-adjustments.  So
> lets define adjustments by "days" for the base datetime object in
> terms of 86400.0 seconds.  A DST aware datetime subclass can then be
> made that does the more complex day-based arithmetic.

Yes.  A "day" is always 24 hours.

--Guido van Rossum (home page: http://www.python.org/~guido/)