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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 _get_current_dup_metrics(self, align_bam):
 """Retrieve duplicate information from input BAM file. """

        metrics_file = "%s.dup_metrics" % os.path.splitext(align_bam)[0]
        if not file_exists(metrics_file):
            dups = 0
            with pysam.Samfile(align_bam, "rb") as bam_handle:
                for read in bam_handle:
                    if (read.is_paired and read.is_read1) or not read.is_paired:
                        if read.is_duplicate:
                            dups += 1
            with open(metrics_file, "w") as out_handle:
                out_handle.write("# custom bcbio-nextgen metrics\n")
                out_handle.write("READ_PAIR_DUPLICATES\t%s\n" % dups)
        return metrics_file