support slice assignment in ListConfig (omry#736)

omegaconf/listconfig.py

@@ -241,7 +241,23 @@ def _set_at_index(self, index: Union[int, slice], value: Any) -> None:
 
     def __setitem__(self, index: Union[int, slice], value: Any) -> None:
         try:
-            self._set_at_index(index, value)
+            if isinstance(index, slice):
+                _ = iter(value)  # check iterable
+                indexes = range(*index.indices(len(self)))
+                if index.step is not None:
+                    # Extended slice assignment lengths must match
+                    if len(indexes) != len(value):
+                        raise ValueError(
+                            f"attempt to assign sequence of size {len(value)} to extended slice of size {len(indexes)}"
+                        )
+                for val_i, i in enumerate(indexes):
+                    del self[i]
+                    self.insert(i, value[val_i])
+                for val_i in range(val_i + 1, len(value)):
+                    i += 1
+                    self.insert(i, value[val_i])
+            else:
+                self._set_at_index(index, value)
         except Exception as e:
             self._format_and_raise(key=index, value=value, cause=e)
 

tests/test_basic_ops_list.py

@@ -845,6 +845,26 @@ def test_getitem_slice(sli: slice) -> None:
     assert olst.__getitem__(sli) == expected
 
 
+def test_setitem_slice() -> None:
+    cfg = OmegaConf.create(["a", "b", "c", "d"])
+    # slice assignment, same number elements
+    assert cfg == ["a", "b", "c", "d"]
+    cfg[1:3] = ["x", "y"]
+    assert cfg == ["a", "x", "y", "d"]
+    # slice assignment, extra elements
+    cfg[1:3] = ["x", "y", "z"]
+    assert cfg == ["a", "x", "y", "z", "d"]
+    # Extended slice assignment
+    cfg[1:3:1] = ["x", "y"]
+    assert cfg == ["a", "x", "y", "z", "d"]
+    # Non iterable
+    with raises(TypeError):
+        cfg[1:3] = 1
+    # Extended slice length mismatch
+    with raises(ValueError):
+        cfg[1:3:1] = ["x", "y", "z"]
+
+
 @mark.parametrize(
     "lst,idx,expected",
     [