Detect out-of-range integer indices in __setitem__ operations

Changelog.rst

@@ -10,6 +10,8 @@ Version NEXTVERSION
   `cfdm.read` (https://github.com/NCAS-CMS/cfdm/issues/355)
 * New function `cfdm.dataset_flatten` that replaces the deprecated*
   `cfdm.netcdf_flatten` (https://github.com/NCAS-CMS/cfdm/issues/355)
+* Raise `IndexError` for out-of-range indices in a value-setting
+  operation on a data array (https://github.com/NCAS-CMS/cfdm/issues/377)
 * New function to control the creation of cached elements during data
   display: `cfdm.display_data`
   (https://github.com/NCAS-CMS/cfdm/issues/363)

cfdm/functions.py

@@ -2517,13 +2517,24 @@ def parse_indices(shape, indices, keepdims=True, newaxis=False):
                 "New axis indices are not allowed"
             )
 
-        if keepdims and isinstance(index, Integral):
+        # Check that any integer indices are in range for the dimension sizes
+        # before integral indices are converted to slices below, for (one for)
+        # consistent behaviour between setitem and getitem. Note out-of-range
+        # slicing works in Python generally (slices are allowed to extend past
+        # end points with clipping applied) so we allow those.
+        integral_index = isinstance(index, Integral)
+        if integral_index and not -size <= index < size:  # could be negative
+            raise IndexError(
+                f"Index {index!r} is out of bounds for axis {i} with "
+                f"size {size}."
+            )
+
+        if integral_index and keepdims:
             # Convert an integral index to a slice
             if index == -1:
                 index = slice(-1, None, None)
             else:
                 index = slice(index, index + 1, 1)
-
         elif hasattr(index, "to_dask_array"):
             to_dask_array = index.to_dask_array
             if callable(to_dask_array):

cfdm/test/test_Data.py

@@ -413,6 +413,22 @@ def test_Data__setitem__(self):
             d[indices] = value
             self.assertEqual((d.array < 0).sum(), 4)
 
+        # Test IndexError emerges for out-of-range indices
+        d = cfdm.Data(np.ones((4, 4)))
+        for indices in (
+            (0, 4),
+            (4, 0),
+            (100, 100),
+            (slice(None), 4),
+            (4, slice(None)),
+            (0, -5),
+            (-5, 0),
+            (-100, -100),
+            (100, -100),
+        ):
+            with self.assertRaises(IndexError):
+                d[indices] = 2
+
     def test_Data_apply_masking(self):
         """Test Data.apply_masking."""
         a = np.ma.arange(12).reshape(3, 4)
@@ -2092,6 +2108,22 @@ def test_Data__getitem__(self):
             (d[0, [4, 0, 3, 1]].array == [[0.018, 0.007, 0.014, 0.034]]).all()
         )
 
+        # Test IndexError emerges for out-of-range indices
+        d = cfdm.Data(np.ones((4, 4)))
+        for indices in (
+            (0, 4),
+            (4, 0),
+            (100, 100),
+            (slice(None), 4),
+            (4, slice(None)),
+            (0, -5),
+            (-5, 0),
+            (-100, -100),
+            (100, -100),
+        ):
+            with self.assertRaises(IndexError):
+                d[indices]
+
     def test_Data_BINARY_AND_UNARY_OPERATORS(self):
         """Test arithmetic, logical and comparison operators on Data."""
         a = np.arange(3 * 4 * 5).reshape(3, 4, 5)