Ensure that cube.shape can only be a tuple (or None).

Author: pp-mo

lib/iris/_data_manager.py

@@ -34,12 +34,16 @@ def __init__(self, data, shape=None):
             dataless.
 
         """
-        if (shape is None) and (data is None):
-            msg = 'one of "shape" or "data" should be provided; both are None'
-            raise ValueError(msg)
-        elif (shape is not None) and (data is not None):
-            msg = '"shape" should only be provided if "data" is None'
-            raise ValueError(msg)
+        if shape is None:
+            if data is None:
+                msg = 'one of "shape" or "data" should be provided; both are None'
+                raise ValueError(msg)
+        else:
+            if data is not None:
+                msg = '"shape" should only be provided if "data" is None'
+                raise ValueError(msg)
+            # Normalise how shape is recorded
+            shape = tuple(shape)
 
         # Initialise the instance.
         self._shape = shape

lib/iris/tests/integration/merge/test_merge_with_dataless.py

@@ -0,0 +1,65 @@
+# Copyright Iris contributors
+#
+# This file is part of Iris and is released under the BSD license.
+# See LICENSE in the root of the repository for full licensing details.
+"""Basic integration tests for merging with dataless cubes."""
+
+import numpy as np
+
+from iris.coords import AuxCoord, DimCoord
+from iris.cube import Cube, CubeList
+
+
+class TestMergeDataless:
+    def _testcube(self, z=1, name="this", dataless=False):
+        # Create a testcube with a scalar Z coord, for merge testing.
+        cube = Cube(
+            [1, 2, 3],
+            long_name=name,
+            dim_coords_and_dims=[(DimCoord([0.0, 1.0, 2], long_name="x"), 0)],
+            aux_coords_and_dims=[(AuxCoord([z], long_name="z"), ())],
+        )
+        if dataless:
+            cube.data = None
+        return cube
+
+    def test_mixed_passthrough(self):
+        # Check that normal merge can handle dataless alongside dataful cubes.
+        cubes = CubeList(
+            [
+                self._testcube(name="this", dataless=False),
+                self._testcube(name="that", dataless=True),
+            ]
+        )
+        result = cubes.merge()
+        assert len(result) == 2
+        cube1, cube2 = [result.extract_cube(name) for name in ("this", "that")]
+        assert not cube1.is_dataless()
+        assert cube2.is_dataless()
+
+    def test_dataless_merge(self):
+        # Check that dataless cubes can be merged.
+        cubes = CubeList(
+            [
+                self._testcube(z=1, dataless=True),
+                self._testcube(z=2, dataless=True),
+            ]
+        )
+        cube = cubes.merge_cube()
+        assert cube.is_dataless()
+        assert np.all(cube.coord("z").points == [1, 2])
+
+    def test_dataless_dataful_merge(self):
+        # Check that dataless cubes can merge **with** regular ones.
+        # Check that dataless cubes can be merged correctly.
+        cubes = CubeList(
+            [
+                self._testcube(z=1, dataless=False),
+                self._testcube(z=2, dataless=True),
+            ]
+        )
+        cube = cubes.merge_cube()
+        assert not cube.is_dataless()
+        data_z1, data_z2 = cube[0].data, cube[1].data
+        assert np.all(data_z1 == [1, 2, 3])
+        assert np.all(np.ma.getmaskarray(data_z2) == True)  # noqa: E712