Return string representation for VCF

def serialize(self):
        """Return string representation for VCF"""
        if self.mate_chrom is None:
            remote_tag = "."
        else:
            if self.within_main_assembly:
                mate_chrom = self.mate_chrom
            else:
                mate_chrom = "<{}>".format(self.mate_chrom)
            tpl = {FORWARD: "[{}:{}[", REVERSE: "]{}:{}]"}[self.mate_orientation]
            remote_tag = tpl.format(mate_chrom, self.mate_pos)
        if self.orientation == FORWARD:
            return remote_tag + self.sequence
        else:
            return self.sequence + remote_tag