PROBLEM SOLVED.

I had defined my python handler as a GET. I changed it to POST, and now it works.
Although I don't understand why it has to be done this way...

I just installed firebug (never used it before).
All I can see is this error message:

POST http://tablsorter.appspot.com/dxx  405 Method Not Allowed  --> this is the url that returns the json data

Response: None

Response Headers
Content-Type   text/html
Allow   GET
Set-Cookie   webpy_session_id=70082469d07d12dc8c875bcbcfa93a87ddcb7918; Path=/
Content-Encoding   gzip
Vary   Accept-Encoding
Date   Mon, 22 Aug 2011 03:49:41 GMT
Server   Google Frontend
Cache-Control   private
Content-Length   24
Request Headers
Host   tablsorter.appspot.com
User-Agent   Mozilla/5.0 (Windows NT 6.1; rv:6.0) Gecko/20100101 Firefox/6.0
Accept   application/json, text/javascript, */*; q=0.01
Accept-Language   en-us,en;q=0.5
Accept-Encoding   gzip, deflate
Accept-Charset   ISO-8859-1,utf-8;q=0.7,*;q=0.7
Connection   keep-alive
X-Requested-With   XMLHttpRequest
Referer   http://tablsorter.appspot.com/static/demo/dgdemo.html
Cookie   webpy_session_id=70082469d07d12dc8c875bcbcfa93a87ddcb7918

I tried all the tutorial samples and I just can't get my grid to work...
If I use a json file as source, they work.
But if I use a json source generated dynamically by a python script, it doesn't work.

I paid special attention to the samples that use a .php page as source.
I guess it's probably a problem of how the json data is formatted.

What could possibly be the problem?

These are some of the failing pages I'm playing with:
http://tablsorter.appspot.com/static/jjj.htm
http://tablsorter.appspot.com/jeasy

Any hint would be highly appreciated...
Luis