Fix: Update IndexSetND.subset retun val to prevent side-effect with IndexSetND.squeeze

Author: samarthmistry

src/docplex_extensions/_index_sets.py

@@ -1312,7 +1312,11 @@ def subset(self, *pattern: Any) -> list[ElemNDT]:
 
         given = tuple(v for v in pattern if v != '*')  # Wildcard filtering
 
-        return self._groupby(*indices)[given]
+        # Use `get` instead of `__getitem__`` because we don't want to update the defaultdict with
+        # an empty list for keys that are not preset prior to returning the empty list. Leads to a
+        # side-effect in `squeeze` because the keys are cached in the defaultdict. So directly
+        # return an empty list with get instead.
+        return self._groupby(*indices).get(given, list())
 
     @overload
     def squeeze(  # numpydoc ignore=GL08

tests/unit_tests/index_sets/indexsetnd_subset_selection_test.py

@@ -366,6 +366,13 @@ def test_squeeze_w_rmvd_elem_pop(input, index, indices, expected):
     assert input.squeeze(*indices) == expected
 
 
+@pytest.mark.parametrize('sub_val', [('*', 1), ('*', 2), (0, '*'), (2, '*')])
+@pytest.mark.parametrize('sqz_idx', [0, 1])
+def test_squeeze_after_subset(setNd_int_cmb2, sub_val, sqz_idx):
+    _ = setNd_int_cmb2.subset(*sub_val)
+    assert_sets_same(setNd_int_cmb2.squeeze(sqz_idx), IndexSet1D(range(2)))
+
+
 def test_squeeze_after_clear(setNd_int_cmb2):
     _ = setNd_int_cmb2.squeeze(0)
     setNd_int_cmb2.clear()