code: def get_frameshift_lengths(num_bins):
      
      fs_len = []
      i = 1
      tmp_bins = 0
      while(tmp_bins<num_bins):
          if i%3:
              fs_len.append(i)
              tmp_bins += 1
          i += 1
      return fs_len
docs: Simple function that returns the lengths for each frameshift category
      if `num_bins` number of frameshift categories are requested.