fix: Table.data support for negative indices

src/magicgui/backends/_qtpy/widgets.py

@@ -1512,8 +1512,35 @@ def _mgui_remove_row(self, row: int) -> None:
     def _mgui_remove_column(self, column: int) -> None:
         self._qwidget.removeColumn(column)
 
+    def _normalize_cell_index(self, row: int, col: int) -> tuple[int, int]:
+        num_rows = self._mgui_get_row_count()
+        num_cols = self._mgui_get_column_count()
+        # Offset negative indices because Qt doesn't natively support them
+        if row < 0:
+            normalized_row = row + num_rows
+        else:
+            normalized_row = row
+        if col < 0:
+            normalized_col = col + num_cols
+        else:
+            normalized_col = col
+        # Qt will not raise an error for attempting to index into an invalid cell, but
+        # normal Python does.
+        if (
+            normalized_row < 0
+            or normalized_col < 0
+            or normalized_row >= num_rows
+            or normalized_col >= num_cols
+        ):
+            raise IndexError(
+                f"Index ({row}, {col}) is out of bounds for table of shape"
+                f" ({num_rows}, {num_cols})."
+            )
+        return normalized_row, normalized_col
+
     def _mgui_get_cell(self, row: int, col: int) -> Any:
         """Get current value of the widget."""
+        row, col = self._normalize_cell_index(row, col)
         item = self._qwidget.item(row, col)
         if item:
             return item.data(_DATA_ROLE)
@@ -1523,6 +1550,7 @@ def _mgui_get_cell(self, row: int, col: int) -> Any:
 
     def _mgui_set_cell(self, row: int, col: int, value: Any) -> None:
         """Set current value of the widget."""
+        row, col = self._normalize_cell_index(row, col)
         if value is None:
             self._qwidget.setItem(row, col, None)
             self._qwidget.removeCellWidget(row, col)

tests/test_table.py

@@ -171,6 +171,8 @@ def test_table_from_numpy():
 INDICES = (
     1,
     (2, 2),
+    -2,
+    (-1, -1),
     (slice(None), 2),
     (slice(None), slice(None)),
     (slice(1, 3), slice(3)),
@@ -181,6 +183,8 @@ def test_table_from_numpy():
 VALUES = (
     (7,) * 4,
     6,
+    (14,) * 4,
+    25,
     (7,) * 6,
     [[1] * 4] * 6,
     [[1] * 3] * 2,
@@ -200,7 +204,7 @@ def test_dataview_getitem(index):
     assert np.allclose(table.data[index], data[index])
 
 
-@pytest.mark.parametrize("index, value", zip(INDICES, VALUES))
+@pytest.mark.parametrize("index, value", tuple(zip(INDICES, VALUES)))
 def test_dataview_setitem(index, value):
     """Test that table.data can be indexed like a numpy array."""
     np = pytest.importorskip("numpy")
@@ -213,6 +217,31 @@ def test_dataview_setitem(index, value):
     assert np.allclose(table.data.to_list(), data)
 
 
+INVALID_INDICES = ((6, 0), (0, 4), (-7, 0), (0, -5))
+
+
+@pytest.mark.parametrize("index", INVALID_INDICES)
+def test_dataview_getitem_invalid_index(index):
+    """Test that invalid cell indices raise IndexError."""
+    np = pytest.importorskip("numpy")
+    data = np.arange(24).reshape(6, 4)
+
+    table = Table(value=data)
+    with pytest.raises(IndexError):
+        table.data[index]
+
+
+@pytest.mark.parametrize("index", INVALID_INDICES)
+def test_dataview_setitem_invalid_index(index):
+    """Test that invalid cell indices raise IndexError."""
+    np = pytest.importorskip("numpy")
+    data = np.arange(24).reshape(6, 4)
+
+    table = Table(value=data)
+    with pytest.raises(IndexError):
+        table.data[index] = 999
+
+
 def test_dataview_delitem():
     """Test that table.data can be indexed like a numpy array."""
     _input = _TABLE_DATA["dict"]