code: def _try_to_clean_garbage(self, writer_spec, exclude_list=()):
      
      # Try to remove garbage (if any). Note that listbucket is not strongly
      # consistent so something might survive.
      tmpl = string.Template(self._TMPFILE_PREFIX)
      prefix = tmpl.substitute(
          id=self.status.mapreduce_id, shard=self.status.shard)
      bucket = self._get_tmp_gcs_bucket(writer_spec)
      account_id = self._get_tmp_account_id(writer_spec)
      for f in cloudstorage.listbucket("/%s/%s" % (bucket, prefix),
                                       _account_id=account_id):
        if f.filename not in exclude_list:
          self._remove_tmpfile(f.filename, self.status.writer_spec)
docs: Tries to remove any files created by this shard that aren't needed.
  
      Args:
        writer_spec: writer_spec for the MR.
        exclude_list: A list of filenames (strings) that should not be
          removed.