How to use the f90nml.findex.FIndex function in f90nml

def test_findex_iteration(self):
        rng = [(None, 5, None)]
        fidx = iter(FIndex(rng))

        for i, j in enumerate(fidx, start=1):
            self.assertEqual(i, j[0])

if not patch_nml:
            patch_nml = Namelist()

        v_name = self.prior_token
        v_values = []

        # Patch state
        patch_values = None

        # Derived type parent index (see notes below)
        dt_idx = None

        if self.token == '(':

            v_idx_bounds = self._parse_indices()
            v_idx = FIndex(v_idx_bounds, self.global_start_index)

            # Update starting index against namelist record
            if v_name.lower() in parent.start_index:
                p_idx = parent.start_index[v_name.lower()]

                for idx, pv in enumerate(zip(p_idx, v_idx.first)):
                    if all(i is None for i in pv):
                        i_first = None
                    else:
                        i_first = min(i for i in pv if i is not None)

                    v_idx.first[idx] = i_first

                # Resize vector based on starting index
                parent[v_name] = prepad_array(parent[v_name], p_idx,
                                              v_idx.first)