code: def concat(self, target, sources, **kwargs):
          
          if isinstance(sources, basestring):
              raise ValueError("sources should be a list")
          if any(',' in s for s in sources):
              raise NotImplementedError("WebHDFS does not support commas in concat")
          response = self._post(target, 'CONCAT', sources=','.join(sources), **kwargs)
          assert not response.content
docs: Concat existing files together.
  
          For preconditions, see
          https://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-common/filesystem/filesystem.html#void_concatPath_p_Path_sources
  
          :param target: the path to the target destination.
          :param sources: the paths to the sources to use for the concatenation.
          :type sources: list