[Python-Dev] Re: dateutil

[Greg Ewing]

Michael Chermside <mcherm at mcherm.com>:

> +0.6  I do not feel as strongly as Greg does that use of +
>       implies an alegbra (because it's glaringly obvious to
>       me that the whole POINT of this library is to deal
>       with the fact that date manipulations do NOT follow
>       any sane algebra).

I wouldn't insist that all uses of '+' be strictly algebraic,
but what we're talking about here is so far from it that I
have trouble thinking of it as any kind of addition operation.

> Perhaps individual transform objects which do just one thing at a time
> but can be combined into a single object which applies them in series:
> 
>     >>> firstCombo = relativeDateDelta([nextMonth, prevDay])
>     >>> secondCombo = relativeDateDelta([prevDay, nextMonth])
>     >>> # or, alternative syntax:
>     >>> firstCombo = nextMonth.andThen(prevDay)

I can't really see the advantage of having a special kind of 
object for this. We already have objects that represent operations 
in Python -- they're called functions! And it's easy to create one 
that combines others:

  def thursday_next_month(d):
    return thursday_of(next_month(d))

Greg Ewing, Computer Science Dept, +--------------------------------------+
University of Canterbury,	   | A citizen of NewZealandCorp, a	  |
Christchurch, New Zealand	   | wholly-owned subsidiary of USA Inc.  |
greg at cosc.canterbury.ac.nz	   +--------------------------------------+