code: def check_signing_key(self):
          
          user_keys = self.gpg.list_keys()
          if len(user_keys) > 0:
              trusted = False
              for key in user_keys:
                  if key['fingerprint'] == self.key_info['fingerprint']:
                      trusted = True
                      logger.debug(("repo signing key trusted in user keyring, "
                                    "fingerprint {0}".format(key['fingerprint'])))
          else:
              trusted = False
          if trusted is False:
              repo_key_url = "{0}/{1}".format(self.url, self.repo_signing_key)
              raise RepositoryUntrustedSigningKeyError(repo_key_url,
                                                       self.key_info['fingerprint'])
docs: Check that repo signing key is trusted by gpg keychain