code: def _vcf_alt(base, other_chr, other_pos, isrc, is_first):
      
      if is_first:
          pipe = "[" if isrc else "]"
          out_str = "{base}{pipe}{chr}:{pos}{pipe}"
      else:
          pipe = "]" if isrc else "["
          out_str = "{pipe}{chr}:{pos}{pipe}{base}"
      return out_str.format(pipe=pipe, chr=other_chr, pos=other_pos + 1,
                            base=base)
docs: Create ALT allele line in VCF 4.1 format associating with other paired end.