There are two types of methods available to the geoprocessing object in Python right now. There are the internal geoprocessing commands, which are what the Geoprocessor Programming Model characterizes, and the geoprocessing tools, which are the same tools available in the ArcToolbox. Unfortunately, the only documentation I can think of about these are from ESRI.

The Geoprocessing Quick Reference guide (PDF) provides a list of all tools available and a short description of each tool. This is similar as running the gp.Usage() on each tool returned by gp.ListTools().

For the programming model… It is hard for my students to grasp it also, and the best explanation I can give is as follows:

The bottom left box labeled arcgisscripting defines the commands available through the geoprocessor (your gp object).
If one of the tools in the above list has an arrow connecting it to another box, it means that the tool returns an object of that type.

For example, to access the geometry of any object, you need to traverse through the following (from the left of the diagram to the right):

gp.SearchCursor() – returns a SearchCursor
SearchCursor.Next() – returns a Row
Row.GetValue() – returns a value from the row, which includes the geometry (called shape)

I hope this is slightly more helpful than the documentation out there.

One question for you. I’m pretty new in geoprocessing in Python for ArcGis and I can’t find a good reference for all the methods availble to geoprocessor. What kind of reference do you use?

Also I don’t quite understand the Geoprocessor Programming Model. Do you have any suggestion where to look for help?