code: def get_fill_char( maf_status ):
      
      ## assert maf_status not in ( maf.MAF_CONTIG_NESTED_STATUS, maf.MAF_NEW_NESTED_STATUS, 
      ##                            maf.MAF_MAYBE_NEW_NESTED_STATUS ), \
      ##     "Nested rows do not make sense in a single coverage MAF (or do they?)"
      if maf_status in ( maf.MAF_NEW_STATUS, maf.MAF_MAYBE_NEW_STATUS, 
                         maf.MAF_NEW_NESTED_STATUS, maf.MAF_MAYBE_NEW_NESTED_STATUS ):
          return "*"
      elif maf_status in ( maf.MAF_INVERSE_STATUS, maf.MAF_INSERT_STATUS ):
          return "="
      elif maf_status in ( maf.MAF_CONTIG_STATUS, maf.MAF_CONTIG_NESTED_STATUS ):
          return "#"
      elif maf_status == maf.MAF_MISSING_STATUS:
          return "X"
      else:
          raise ValueError("Unknwon maf status")
docs: Return the character that should be used to fill between blocks
      having a given status