Q:

Is there a python web framework/toolkit that provides client-side form validation? 

There are a lot of tools to build html forms using python1.   Most of these provide a means to do form validation, but only on the server side (i.e., after the submit button is pressed).   Are there any ways to implement a client-side form validation in python?   Do client-side operations this complicated require JavaScript? 
1 for example: https://wiki.python.org/moin/WebComponents

A:

The web2py framework has client-side validation options. 
There is a plugin called plugin_ValidationEngine that implements server-side validators on the client side, and powerformwizard (see https://bitbucket.org/rochacbruno/powerformwizard/overview) does something similar in a wizard-steps kind of format. 
There may be others -- there are numerous contributed plug-ins for web2py.