def validate(self, *args, **kwargs):
    if not 'recaptcha_challenge_field' in kwargs:
        return 'no recaptcha_challenge_field'
if not 'recaptcha_response_field' in kwargs:
    return 'no recaptcha_response_field'
recaptcha_challenge_field = kwargs['recaptcha_challenge_field']
recaptcha_response_field = kwargs['recaptcha_response_field']
response = captcha.submit(recaptcha_challenge_field,
    recaptcha_response_field, 'private_key_string_you_got_from_recaptcha',
    cherrypy.request.headers['Remote-Addr'])
if response.is_valid:
    raise cherrypy.HTTPRedirect('success_page')
if response.error_code:
    raise cherrypy.HTTPRedirect('display_recaptcha?error=%s' % response.
        error_code)
How to use Python plugin reCaptcha client for validation?