code: def logout(self, auth_secret):
          
          result = {pytwis_constants.ERROR_KEY: None}
  
          # Check if the user is logged in.
          loggedin, userid = self._is_loggedin(auth_secret)
          if not loggedin:
              result[pytwis_constants.ERROR_KEY] = pytwis_constants.ERROR_NOT_LOGGED_IN
              return (False, result)
  
          # Generate the new authentication secret.
          new_auth_secret = secrets.token_hex()
  
          # Replace the old authentication secret by the new one.
          userid_profile_key = pytwis_constants.USER_PROFILE_KEY_FORMAT.format(userid)
          with self._rc.pipeline() as pipe:
              pipe.multi()
              pipe.hset(userid_profile_key, pytwis_constants.AUTH_KEY, new_auth_secret)
              pipe.hset(pytwis_constants.AUTHS_KEY, new_auth_secret, userid)
              pipe.hdel(pytwis_constants.AUTHS_KEY, auth_secret)
              pipe.execute()
  
          result[pytwis_constants.USERNAME_KEY] = \
              self._rc.hget(userid_profile_key, pytwis_constants.USERNAME_KEY)
          result[pytwis_constants.AUTH_KEY] = ''
          return (True, result)
docs: Log out of a user.
  
          Parameters
          ----------
          auth_secret: str
              The authentication secret of the logged-in user.
  
          Returns
          -------
          bool
              True if the logout is successful, False otherwise.
          result
              None if the logout is successful, a dict containing the error string
              with the key ERROR_KEY otherwise.
  
          Note
          ----
          Possible error strings are listed as below:
  
          -  ERROR_NOT_LOGGED_IN