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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 open_reader(self, file_name, reopen=False, endpoint=None, start=None, length=None, **kwargs):
 """ Open a volume file for read. A file-like object will be returned which can be used to read contents from volume files. :param str file_name: name of the file :param bool reopen: whether we need to open an existing read session :param str endpoint: tunnel service URL :param start: start position :param length: length limit :param compress_option: the compression algorithm, level and strategy :type compress_option: :class:`odps.tunnel.CompressOption` :Example: """

        tunnel = self._create_volume_tunnel(endpoint=endpoint)
        download_id = self._download_id if not reopen else None
        download_session = tunnel.create_download_session(volume=self.volume.name, partition_spec=self.name,
                                                          file_name=file_name, download_id=download_id, **kwargs)
        self._download_id = download_session.id

        open_args = {}
        if start is not None:
            open_args['start'] = start
        if length is not None:
            open_args['length'] = length
        return download_session.open(**open_args)