[Python-ideas] the Quantity pattern

[Darren Dale]

On Tue, Mar 2, 2010 at 2:17 PM, Robert Kern <robert.kern at gmail.com> wrote:
> On 2010-03-02 12:35 PM, Bill Janssen wrote:
>>
>> I was looking at Martin Fowler's Quantity pattern earlier.
>>
>> http://martinfowler.com/ap2/quantity.html
>>
>> I remember writing this up as an idea for Fortran back in the early
>> 80's, only to find a CACM paper from 1978 exploring the idea:
>> "Incorporation of Units into Programming Languages", Karr&  Loveman, May
>> 1978.
>>
>> But it would still be a cool idea for Python.  Perhaps it's already
>> there and I haven't noticed?
>
> Tons of implementations (in no particular order):
>
> http://pypi.python.org/pypi/quantities/
> http://pypi.python.org/pypi/Unum/
> http://pypi.python.org/pypi/magnitude/
> http://pypi.python.org/pypi/units/
> http://pypi.python.org/pypi/ScientificPython/
> http://pypi.python.org/pypi/SciMath/
>
> And quite a few more that are part of other packages or otherwise not on
> PyPI. It's ridiculously easy to write something that what people think are
> the common cases and so everyone does. It's a lot harder to write something
> that robustly handles what are actually common cases (absolute temperature
> scales, logarithmic scales, etc.).

I prefer to think of this as two separate issues. One issue is a
Quantity pattern for dealing with values that have magnitude and
dimensionality, and the other is coordinate systems (requiring a point
of reference, like temperature scales).

Darren