How to use the bamnostic.csi.CsiBin function in bamnostic

"""
        bins = None if idx else {}

        for b in range(n_bins):
            bin_id, loffset, n_chunks = unpack_bid_loffset_nchunk(self._io.read(16))
            if idx:
                if bin_id == self._UNMAP_BIN:
                    assert n_chunks == 2, 'Bin 3740 is supposed to have 2 chunks. This has {}'.format(n_chunks)
                    unmapped = bai.Unmapped(*unpack_unmapped(self._io.read(32)))
                    self.unmapped[ref_id] = unmapped
                else:
                    if not n_chunks == 0:
                        self._io.seek(16 * n_chunks, 1)
            else:
                chunks = self.get_chunks(n_chunks)
                bins[bin_id] = CsiBin(loffset, chunks)
        else:
            return bins