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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 _postprocess_variants(record_file, data, ref_file, out_file):
 """Post-process variants, converting into standard VCF file. """

    if not utils.file_uptodate(out_file, record_file):
        with file_transaction(data, out_file) as tx_out_file:
            cmd = ["dv_postprocess_variants.py", "--ref", ref_file,
                   "--infile", record_file, "--outfile", tx_out_file]
            do.run(cmd, "DeepVariant postprocess_variants %s" % dd.get_sample_name(data))
    return out_file