[SolutionArray] Disallow empty extra columns

If the extra columns are passed to the SolutionArray, they must either
have initial values or the SolutionArray must be empty.

interfaces/cython/cantera/composite.py

@@ -544,14 +544,18 @@ def __init__(self, phase, shape=(0,), states=None, extra=None, meta=None):
                     raise ValueError("Unable to map extra SolutionArray "
                                      "input named {!r}".format(name))
         elif extra is not None:
+            if self._shape != (0,):
+                raise ValueError("Initial values for extra properties must be "
+                                 "supplied in a dictionary if the SolutionArray "
+                                 "is not initially empty.")
             if isinstance(extra, np.ndarray):
                 extra = extra.flatten()
             elif isinstance(extra, str):
                 extra = [extra]
 
             try:
                 iter_extra = iter(extra)
-            except TypeError :
+            except TypeError:
                 raise ValueError(
                     "Extra properties can be created by passing an iterable "
                     "of names for the properties. If you want to supply initial "
@@ -568,7 +572,7 @@ def __init__(self, phase, shape=(0,), states=None, extra=None, meta=None):
                     raise ValueError(
                         "Unable to create extra column '{}': name is already "
                         "used by SolutionArray objects.".format(name))
-                self._extra[name] = np.empty(self._shape)
+                self._extra[name] = np.empty(shape=(0,))
 
         if meta is None:
             self._meta = {}

interfaces/cython/cantera/test/test_thermo.py

@@ -1745,6 +1745,15 @@ def test_extra_no_shape(self):
         self.assertEqual(states.prop.shape, (2, 2))
         self.assertArrayNear(states.prop, np.array(((3, 3), (3, 3))))
 
+    def test_extra_not_empty(self):
+        """Test that a non-empty SolutionArray raises a ValueError if
+           initial values for properties are not supplied.
+        """
+        with self.assertRaisesRegex(ValueError, "Initial values for extra properties"):
+            ct.SolutionArray(self.gas, 3, extra=["prop"])
+        with self.assertRaisesRegex(ValueError, "Initial values for extra properties"):
+            ct.SolutionArray(self.gas, 3, extra=np.array(["prop", "prop2"]))
+
     def test_extra_wrong_shape(self):
         with self.assertRaisesRegex(ValueError, "Unable to map"):
             ct.SolutionArray(self.gas, (3, 3), extra={"prop": np.arange(3)})
@@ -1784,10 +1793,10 @@ def test_assign_to_slice(self):
 
     def test_extra_create_by_ndarray(self):
         properties_array = np.array(["prop1", "prop2", "prop3"])
-        states = ct.SolutionArray(self.gas, shape=(2, 6, 9), extra=properties_array)
-        self.assertEqual(states.prop1.shape, (2, 6, 9))
-        self.assertEqual(states.prop2.shape, (2, 6, 9))
-        self.assertEqual(states.prop3.shape, (2, 6, 9))
+        states = ct.SolutionArray(self.gas, shape=(0,), extra=properties_array)
+        self.assertEqual(states.prop1.shape, (0,))
+        self.assertEqual(states.prop2.shape, (0,))
+        self.assertEqual(states.prop3.shape, (0,))
         # Ensure that a 2-dimensional array is flattened
         properties_array = np.array((["prop1"], ["prop2"]))
         states = ct.SolutionArray(self.gas, extra=properties_array)