code: def _sendFiles(
          self, files, message=None, thread_id=None, thread_type=ThreadType.USER
      ):
          
          thread_id, thread_type = self._getThread(thread_id, thread_type)
          data = self._getSendData(
              message=self._oldMessage(message),
              thread_id=thread_id,
              thread_type=thread_type,
          )
  
          data["action_type"] = "ma-type:user-generated-message"
          data["has_attachment"] = True
  
          for i, (file_id, mimetype) in enumerate(files):
              data["{}s[{}]".format(mimetype_to_key(mimetype), i)] = file_id
  
          return self._doSendRequest(data)
docs: Sends files from file IDs to a thread
  
          `files` should be a list of tuples, with a file's ID and mimetype