Recommendation for python form validation library
it depends on what underlying framework you use.
for django , built in form framework is best, 
while kay uses extended version of zine's form system
and tipfy uses WTForms.  
django's built in system is best so far . 
what framework do you use under the hood ?
I would like a form validation library that
1.separate html generation from form validation;
2.validation errors can be easily serialized, eg. dumped as a json object
What form validation library would you choose in a python web project?