code: def get_user(self, username):
          
          if hasattr(self._bot, 'user_manager'):
              user = self._bot.user_manager.get_by_username(username)
              if user:
                  return user
              user = SlackUser.get_user(self._bot.sc, username)
              self._bot.user_manager.set(user)
              return user
          return SlackUser.get_user(self._bot.sc, username)
docs: Utility function to query slack for a particular user
  
          :param username: The username of the user to lookup
          :return: SlackUser object or None