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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def concat(self, target, sources, **kwargs):
 """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 """

        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