This is an extension of ochiba77's slice here.  The issue I had is that the data that contained the fields for the slice were available to me via a web service call, not in a database.  I modified his code as follows.  The view feels a little hacky...  but I've never done any web development, and it works, so it's good enough for a prototype.  

Here's the controller...  I had a main category of two segments...  when one of those is chosen, I needed to get the materials corresponding to the chosen segment via a web service call.  getMats is the function for that.

def shouldcost4():  
    segments = ['Castings', 'Forgings'] #category = segment
    if request.vars.segment_name:
        materials = getMats(segments[int(request.vars.segment_name)])
    else:
        materials = getMats(segments[0])
    if request.vars.material_name:  #maker == material
        ret_string = request.vars.segment_name + ' | ' + request.vars.material_name
    else:
        ret_string = 'a'   
    return dict(segments=segments, materials=materials, ret_string=ret_string)

Here's my A_Widgets.py file with the getMats function...

import uuid
import datetime
from httplib2 import Http
from urllib import urlencode
import json

import json, urllib2
def getMats(segment):
    u = urllib2.urlopen('URL_GOES_HERE?Segment='+segment)        
    j = json.load(u)['results']
    mats = [str(j[a]['MATERIALSPEC']) for a in range(len(j))]      
    return(mats)

And my view...

{{extend 'layout.html'}}
{{segments=segments}}
{{materials=materials}}


<form enctype="multipart/form-data" action="{{URL()}}" method="post">
    <label for="part_number">Part Number:</label>
    <input type="text" name="part_number" value={{=request.vars.part_number}}><div />
    <label for="segment_name">Segment Name:</label>
    <select name='segment_name' 
        onchange="jQuery(material_name).remove();jQuery(matlabel).remove();
        ajax('material', ['segment_name'], 'shadow_clone');">             
        {{for i in range(len(segments)):}}
            <option value="{{=i}}" 
                {{=" selected='selected'" if str(i)==request.vars.segment_name else ""}}>
            {{=segments[i]}}
            </option>
        {{pass}}
    </select> <div />
    <span id='shadow_clone'></span>
    <label id="matlabel" for="material_name">Material:</label>
    <select name='material_name' >
        {{for i in range(len(materials)):}}
            <option value="{{=i}}" 
                {{=XML(" selected='selected'") if str(i)==request.vars.material_name else ""}}>
            {{=materials[i]}}</option>
        {{pass}}
    </select><div />
    <label for="EAU">Estimated Annual Usage:</label>
    <input type="text" name="EAU" value={{=request.vars.EAU}}><div />
    
    <input type="submit">  
</form>

<div />

And here's what it looks like...

That's it.  

cn