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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 run_tnscope(align_bams, items, ref_file, assoc_files, region=None, out_file=None):
 """Call variants with Sentieon's TNscope somatic caller. """

    if out_file is None:
        out_file = "%s-variants.vcf.gz" % utils.splitext_plus(align_bams[0])[0]
    if not utils.file_exists(out_file):
        variant_regions = bedutils.population_variant_regions(items, merged=True)
        interval = _get_interval(variant_regions, region, out_file, items)
        with file_transaction(items[0], out_file) as tx_out_file:
            paired = vcfutils.get_paired_bams(align_bams, items)
            assert paired and paired.normal_bam, "Require normal BAM for Sentieon TNscope"
            dbsnp = "--dbsnp %s" % (assoc_files.get("dbsnp")) if "dbsnp" in assoc_files else ""
            license = license_export(items[0])
            cores = dd.get_num_cores(items[0])
            cmd = ("{license}sentieon driver -t {cores} -r {ref_file} "
                   "-i {paired.tumor_bam} -i {paired.normal_bam} {interval} "
                   "--algo TNscope "
                   "--tumor_sample {paired.tumor_name} --normal_sample {paired.normal_name} "
                   "{dbsnp} {tx_out_file}")
            do.run(cmd.format(**locals()), "Sentieon TNscope")
    return out_file