code: def colwise_diag_idxs(size, num=2):
      r
      import utool as ut
      diag_idxs = ut.iprod(*[range(size) for _ in range(num)])
      upper_diag_idxs = [
          tup[::-1] for tup in diag_idxs
          if all([a > b for a, b in ut.itertwo(tup)])
      ]
      return upper_diag_idxs