question on setting choice values in a grid

Howdy,

I am having trouble bootstrapping my knowledge of grids. I want to use a choice editor in a cell, but
to have the choices change dynamically based on contents of another cell (also a choice editor).

I can not figure out the API for changing the choices. I do not know if this is the best way to do it, but I am
basing my code on the gridCustTable.py demo

class CustomDataTable(gridlib.PyGridTableBase):
     def __init__(self, log):
         gridlib.PyGridTableBase.__init__(self)

         self.colLabels = ['field1', 'field2']

         self.dataTypes = [
                           gridlib.GRID_VALUE_CHOICE ,
                           ]
  ...

notice that I have left the "+ ':a,b,c,..' " off the dataTypes with the intention of setting them later.
Can anyone point out the API how I do this? Also, I find the self.dataTypes behavior completely
undocumented. Can someone point out either documentation or else where the source code lives?

thanks,
Danny