code: def get_chatlist(chatfile):
      
      if not chatfile:
          return set()
      try:
          with open(chatfile) as file_contents:
              return set(int(chat) for chat in file_contents)
      except (OSError, IOError) as exc:
          LOGGER.error('could not load saved chats:\n%s', exc)
          return set()
docs: Try reading ids of saved chats from file.
      If we fail, return empty set