<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _attempt_resumable_download(self, key, fp, headers, cb, num_cb, torrent, version_id):
 """ Attempts a resumable download. Raises ResumableDownloadException if any problems occur. """

        cur_file_size = get_cur_file_size(fp, position_to_eof=True)

        if (cur_file_size and 
            self.etag_value_for_current_download and
            self.etag_value_for_current_download == key.etag.strip('"\'')):
            # Try to resume existing transfer.
            if cur_file_size > key.size:
              raise ResumableDownloadException(
                  '%s is larger (%d) than %s (%d).\nDeleting tracker file, so '
                  'if you re-try this download it will start from scratch' %
                  (fp.name, cur_file_size, str(storage_uri_for_key(key)),
                   key.size), ResumableTransferDisposition.ABORT)
            elif cur_file_size == key.size:
                if key.bucket.connection.debug >= 1:
                    print 'Download complete.'
                return
            if key.bucket.connection.debug >= 1:
                print 'Resuming download.'
            headers = headers.copy()
            headers['Range'] = 'bytes=%d-%d' % (cur_file_size, key.size - 1)
            cb = ByteTranslatingCallbackHandler(cb, cur_file_size).call
            self.download_start_point = cur_file_size
        else:
            if key.bucket.connection.debug >= 1:
                print 'Starting new resumable download.'
            self._save_tracker_info(key)
            self.download_start_point = 0
            # Truncate the file, in case a new resumable download is being
            # started atop an existing file.
            fp.truncate(0)

        # Disable AWSAuthConnection-level retry behavior, since that would
        # cause downloads to restart from scratch.
        key.get_file(fp, headers, cb, num_cb, torrent, version_id,
                     override_num_retries=0)
        fp.flush()