![](https://secure.gravatar.com/avatar/ec366db3649cf13f4061b519193849d6.jpg?s=120&d=mm&r=g)
Duncan Child wrote:
1) any interest out there in us putting a units package into scipy?
Sure, but not any of the current ones.
2) any preference for a particular implementation? Unum, etc.
Unum is GPL. I don't think any of the current offerings (Unum, ScientificPython's PhysicalQuantities, and pyre.units) do particularly well with this issue, although, as I note below, PhysicalQuantities gets closest.
3) does anyone have input or suggestions regarding the temperature issue?
Personally: computing absolute "degrees Fahrenheit" from absolute "degrees Celsius" is not a unit conversion; it is a calculation built on top of unit conversions. Converting "feet" from "meters" is a unit conversion. Computing "feet from my house" from "meters from the North Pole" is a calculation. I think that it is unwise to expect a unit conversion system to handle such a computation the same way it handles everything else. That said, ScientificPython hacks around this creditably: "K" and "degR" are both the absolute (referenced to absolute zero) and the differential units. "degC" and "degF" are the absolute units referenced to their respective zeros. It's limited, though. You can't add a "degR" differential temperature to a "degC" absolute temperature, but you can add a "K" differential temperature. You can add "degC" to a "degC", but that's inconsistent. Frink[1], which I hold as the gold standard for computer unit conversions (and whose "Sample Calculations"[2] ought to be repeated for any proposed unit package), sorta gets this right. Celsius[x] and Fahrenheit[x] are functions that go back and forth between systems. Give them an unadorned number, they'll interpret as, e.g. "10 degrees Celsius", and convert to absolute Kelvin. Give it an absolute temperature (in Kelvin or Rankine), and it will spit out the numerical value of the temperature in its own scale (although unadorned by any unit). "degC" and "degF" are the differential units. It would be useful to have a system that would handle the general case of referenced measurements like the Celsius and Fahrenheit scales and "meters from my house". The appropriate distinctions should be made when operations mix referenced measurements and "differential" quantities. Oh, and any system should yoink the contents of Frink's database. [1] http://futureboy.homeip.net/frinkdocs/ [2] http://futureboy.homeip.net/frinkdocs/#SampleCalculations -- Robert Kern rkern@ucsd.edu "In the fields of hell where the grass grows high Are the graves of dreams allowed to die." -- Richard Harter