def __init__(self, urls, chunksize, total_size=None, client=None):
        super(ChunkedURLWriter, self).__init__()
        self._urls = urls
        self._chunksize = chunksize
        self._url_idx = 0
        self.init_client(client)
        self.bytes_written = 0
        self.total_size = total_size
        self.etags = []  # type: List[str]