code: def get_sender(doc):
          
          key_id = doc.find(".//{%s}sig" % NAMESPACE).get("key_id")
          return urlsafe_b64decode(key_id).decode("utf-8")
docs: Get the key_id from the `sig` element which contains urlsafe_b64encoded Diaspora handle.
  
          :param doc: ElementTree document
          :returns: Diaspora handle