About the “javascript support for form.py” idea?
Kai Hendry suggest me to see this specification (Web Form 2.0).

This specification gives some Form validation types , including date, email, range , etc.

These types of validation might be implemented by browser someday. And It also provides an customer validate attribute.

I don’t think I can implement the Web Form 2.0 in 3 month.

Before this specification is implemented, a javascript validation framework is still useful.
And
Even this specification is implemented, I think this kind of javascript
will be needed in some time. For example, validation relate to more
than one fields.( eg. One filed is required only anther check-box has
been checked.)