Simple Recaptcha validation method when using Google App Engine (GAE), Webapp2 and WTForms.

recaptcha_validate.py

  def validate_captcha(self, form):
    recaptcha_challenge_field = self.request.get("recaptcha_challenge_field")
    recaptcha_response_field = self.request.get("recaptcha_response_field")
    remote_ip = self.request.remote_addr
    recaptcha_private_key = 'MY_PRIVATE_KEY' # put recaptcha private key here

    recaptcha_post_data = {"privatekey":  recaptcha_private_key,
        "remoteip": remote_ip,
        "challenge": recaptcha_challenge_field,
        "response": recaptcha_response_field}
    response = urlfetch.fetch(url='http://www.google.com/recaptcha/api/verify', payload=urlencode(recaptcha_post_data), method="POST")
    captcha_ok = True if response.content.split("\n")[0] == "true" else False
    if not captcha_ok:
      form.captcha.errors.append("Invalid captcha values, please try again")
    return captcha_ok

The HTML fragment that generates the form fields needed for this to work is here:

https://gist.github.com/mengelhart/8045070