def signature(self):
        """
        create a unique signature for any GFF line based on joining
        columns 1,2,3,4,5,7,8 (into a comma separated string)
        """
        sig_elems = [self.seqid, self.source, self.type, \
                    self.start, self.end, self.strand, \
                    self.phase]
        if re.search("exon|CDS|UTR", self.type):
            parent = self.get_attr("Parent")
            if parent:
                (locus, iso) = atg_name(parent, retval="locus,iso", \
                        trimpad0=False)
                if locus:
                    sig_elems.append(locus)
        else:
            sig_elems.extend([self.accn])

        return ",".join(str(elem) for elem in sig_elems)
create a unique signature for any GFF line based on joining
        columns 1,2,3,4,5,7,8 (into a comma separated string)