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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 _normalize_sv_coverage_gatk(group_id, inputs, backgrounds, work_dir, back_files, out_files):
 """Normalize CNV coverage using panel of normals with GATK's de-noise approaches. """

    input_backs = set(filter(lambda x: x is not None,
                             [dd.get_background_cnv_reference(d, "gatk-cnv") for d in inputs]))
    if input_backs:
        assert len(input_backs) == 1, "Multiple backgrounds in group: %s" % list(input_backs)
        pon = list(input_backs)[0]
    elif backgrounds:
        pon = gatkcnv.create_panel_of_normals(backgrounds, group_id, work_dir)
    else:
        pon = None
    for data in inputs:
        work_dir = utils.safe_makedir(os.path.join(dd.get_work_dir(data), "structural",
                                                   dd.get_sample_name(data), "bins"))
        denoise_file = gatkcnv.denoise(data, pon, work_dir)
        out_files[dd.get_sample_name(data)] = denoise_file
        back_files[dd.get_sample_name(data)] = pon
    return back_files, out_files