python-quantities-developers team mailing list archive

[Darren Dale <dsdale24@xxxxxxxxx>]

Hi Tony,

On Sun, Jul 12, 2009 at 12:53 PM, Tony S Yu <tonyyu@xxxxxxx> wrote:

> Hi Darren,
> On Jul 11, 2009, at 6:44 PM, Darren Dale wrote:
>
> Please take a moment to consider the following, which is included in the
> tutorial at http://packages.python.org/quantities/user/tutorial.html :
>
> ---
> One final note: Quantities is not a package for describing coordinate
> systems that require a point of reference, like positions on a map or
> absolute temperature scales. Proper support of coordinate systems would be a
> fairly large undertaking and is outside the scope of this project.
> ---
>
> I would argue that the current behavior is correct, because quantities
> assumes that degC (for example) is a temperature difference, not an absolute
> temperature. So I would opt not to apply this patch.
>
>
> Hmm, I think I read this note when I first started using quantities, but I
> completely forgot about it. I agree that this feature would be pretty
> difficult to add and understand why it'd be out of the scope of this
> project. (Now that I think about it, I can't imagine how one would
> distinguish between temp differences and absolute temps).
>

I was originally resistant to suggestions on the scipy mailing list that
quantities should not try to support coordinate systems. But one commentor
brought up general relativity and tensor transformations, and that was
enough to convince me.


> However, I think this would be a common "gotcha" for users who want to
> convert temperatures, and deserves a slightly more prominent mention than
> the note above. FWIW, I would suggest putting the "One final note" under a
> restructuredtext admonition (maybe, "important" or "attention" with
> appropriate styling to give it emphasis).
>


That's a good suggestion, Would you consider registering a branch and merge
request at launchpad? See https://help.launchpad.net/Code/Review . I had a
hard time finding the link to register a merge request, it turned out I was
not logged in so the branch overview page didn't recognize me as the owner
of the branch. We have not made good use of Launchpad's mechanisms in the
past, but I have been following the bzr mailing list for a while and have
been very impressed with their process, and would like to get to a point
where my own work is reviewed by other developers before it gets merged into
the trunk.

Darren