Use sambamba to slice a bam region

def _slice_bam(in_bam, region, tmp_dir, config):
    """Use sambamba to slice a bam region"""
    name_file = os.path.splitext(os.path.basename(in_bam))[0]
    out_file = os.path.join(tmp_dir, os.path.join(tmp_dir, name_file + _to_str(region) + ".bam"))
    sambamba = config_utils.get_program("sambamba", config)
    region = _to_sambamba(region)
    with file_transaction(out_file) as tx_out_file:
        cmd = ("{sambamba} slice {in_bam} {region} -o {tx_out_file}")
        do.run(cmd.format(**locals()), "Slice region", {})
    return out_file