[Proj] Length of a deg in metres

[Nicolas Cadieux]

Hi,

I am writing to python code to calculate the length (in metres) of a 
degree of longitude at a certain degree of latitude.  I would like to 
take various ellipsoid in mind (WGS84, GRS80, Clarke 1866...).  The goal 
is to find the right scale (or z factor) when making slope or shade 
raster models when x and y are in long/lat and z in feet or meters.  Can 
someone point me in the right direction to do this in using Proj?  Is 
Proj the best option for this?

Thanks,

Nicolas