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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 _prep_config(items, paired, work_dir):
 """Run initial configuration, generating a run directory for Manta. """

    assert utils.which("configManta.py"), "Could not find installed configManta.py"
    out_file = os.path.join(work_dir, "runWorkflow.py")
    if not utils.file_exists(out_file) or _out_of_date(out_file):
        config_script = os.path.realpath(utils.which("configManta.py"))
        cmd = [utils.get_program_python("configManta.py"), config_script]
        if paired:
            if paired.normal_bam:
                cmd += ["--normalBam=%s" % paired.normal_bam, "--tumorBam=%s" % paired.tumor_bam]
            else:
                cmd += ["--tumorBam=%s" % paired.tumor_bam]
        else:
            cmd += ["--bam=%s" % dd.get_align_bam(data) for data in items]
        data = paired.tumor_data if paired else items[0]
        cmd += ["--referenceFasta=%s" % dd.get_ref_file(data), "--runDir=%s" % work_dir]
        if dd.get_coverage_interval(data) not in ["genome"]:
            cmd += ["--exome"]
        for region in _maybe_limit_chromosomes(data):
            cmd += ["--region", region]
        resources = config_utils.get_resources("manta", data["config"])
        if resources.get("options"):
            cmd += [str(x) for x in resources["options"]]
        # If we are removing polyX, avoid calling on small indels which require
        # excessively long runtimes on noisy WGS runs
        if "polyx" in dd.get_exclude_regions(data):
            cmd += ["--config", _prep_streamlined_config(config_script, work_dir)]
        do.run(cmd, "Configure manta SV analysis")
    return out_file