code: def _total_jxn_counts(fns):
      
      df = pd.read_table(fns[0], header=None, names=COLUMN_NAMES)
      df.index = (df.chrom + ':' + df.start.astype(int).astype(str) + '-' +
                  df.end.astype(int).astype(str))
      counts = df.unique_junction_reads
      for fn in fns[1:]:
          df = pd.read_table(fn, header=None, names=COLUMN_NAMES)
          df.index = (df.chrom + ':' + df.start.astype(int).astype(str) + '-' +
                      df.end.astype(int).astype(str))
          counts = counts.add(df.unique_junction_reads, fill_value=0)
      return counts
docs: Count the total unique coverage junction for junctions in a set of
      SJ.out.tab files.