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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 _bam_coverage(name, bam_input, data):
 """Run bamCoverage from deeptools"""

    cmd = ("{bam_coverage} -b {bam_input} -o {bw_output} "
          "--binSize 20 --effectiveGenomeSize {size} "
          "--smoothLength 60 --extendReads 150 --centerReads -p {cores}")
    size = bam.fasta.total_sequence_length(dd.get_ref_file(data))
    cores = dd.get_num_cores(data)
    try:
        bam_coverage = config_utils.get_program("bamCoverage", data)
    except config_utils.CmdNotFound:
        logger.info("No bamCoverage found, skipping bamCoverage.")
        return None
    resources = config_utils.get_resources("bamCoverage", data["config"])
    if resources:
        options = resources.get("options")
        if options:
            cmd += " %s" % " ".join([str(x) for x in options])
    bw_output = os.path.join(os.path.dirname(bam_input), "%s.bw" % name)
    if utils.file_exists(bw_output):
        return bw_output
    with file_transaction(bw_output) as out_tx:
        do.run(cmd.format(**locals()), "Run bamCoverage in %s" % name)
    return bw_output