docs: def key_from_keybase(username, fingerprint=None):
      """Look up a public key from a username"""
      url = keybase_lookup_url(username)
      resp = requests.get(url)
      if resp.status_code == 200:
          j_resp = json.loads(polite_string(resp.content))
          if 'them' in j_resp and len(j_resp['them']) == 1:
              kb_obj = j_resp['them'][0]
              if fingerprint:
                  return fingerprint_from_keybase(fingerprint, kb_obj)
              else:
                  if 'public_keys' in kb_obj \
                     and 'pgp_public_keys' in kb_obj['public_keys']:
                      key = kb_obj['public_keys']['primary']
                      return massage_key(key)
  
      return None