<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def detect_complexity(bam_in, genome, out):
 """ genome coverage of small RNA """

    if not genome:
        logger.info("No genome given. skipping.")
        return None
    out_file = op.join(out, op.basename(bam_in) + "_cov.tsv")
    if file_exists(out_file):
        return None
    fai = genome + ".fai"
    cov = pybedtools.BedTool(bam_in).genome_coverage(g=fai, max=1)
    cov.saveas(out_file)
    total = 0
    for region in cov:
        if region[0] == "genome" and int(region[1]) != 0:
            total += float(region[4])
    logger.info("Total genome with sequences: %s " % total)