[Thermo] Clarify extra items from iterables

Make sure that ndarrays are one-dimensional. Move check for bare string.
Clarify error messages. Reduce indentation. Add tests for creating extra
items from bare strings and ndarrays.

interfaces/cython/cantera/composite.py

@@ -529,9 +529,6 @@ def __init__(self, phase, shape=(0,), states=None, extra=None, meta=None):
 
         self._extra = OrderedDict()
 
-        if isinstance(extra, str):
-            extra = [extra]
-
         if isinstance(extra, dict):
             for name, v in extra.items():
                 if name in reserved:
@@ -546,28 +543,31 @@ 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 isinstance(extra, np.ndarray):
+                extra = extra.flatten()
+            elif isinstance(extra, str):
+                extra = [extra]
+
             try:
                 iter_extra = iter(extra)
             except TypeError :
                 raise ValueError(
                     "Extra properties can be created by passing an iterable "
-                    "of names for the properties, if the SolutionArray is not initially "
-                    "empty. If you want to supply initial values for the properties, use "
-                    "a dictionary whose keys are the names of the properties and values "
-                    "are the initial values.") from None
+                    "of names for the properties. If you want to supply initial "
+                    "values for the properties, use a dictionary whose keys are "
+                    "the names of the properties and values are the initial "
+                    "values.") from None
 
             for name in iter_extra:
-                if isinstance(name, str):
-                    if name in reserved:
-                        raise ValueError(
-                            "Unable to create extra column '{}': name is already "
-                            "used by SolutionArray objects.".format(name))
-                    self._extra[name] = np.empty(self._shape)
-
-                else:
+                if not isinstance(name, str):
                     raise TypeError(
-                        "Unable to create extra column, passed value {}: "
+                        "Unable to create extra column, passed value '{!r}' "
                         "is not a string".format(name))
+                if name in reserved:
+                    raise ValueError(
+                        "Unable to create extra column '{}': name is already "
+                        "used by SolutionArray objects.".format(name))
+                self._extra[name] = np.empty(self._shape)
 
         if meta is None:
             self._meta = {}

interfaces/cython/cantera/test/test_thermo.py

@@ -1720,6 +1720,10 @@ def test_extra_reserved_names(self):
         with self.assertRaisesRegex(ValueError, "name is already used"):
             ct.SolutionArray(self.gas, extra={"creation_rates": 0})
 
+    def test_extra_create_by_string(self):
+        states = ct.SolutionArray(self.gas, extra="prop")
+        self.assertEqual(states.prop.shape, (0,))
+
     def test_assign_to_slice(self):
         states = ct.SolutionArray(self.gas, 7, extra={'prop': range(7)})
         array = np.arange(7)
@@ -1729,24 +1733,17 @@ def test_assign_to_slice(self):
         array_mod = np.array([0, -5, 2, 0, 1, 5, 6])
         self.assertArrayNear(states.prop, array_mod)
 
-    def test_extra2(self):
-        states = ct.SolutionArray(self.gas, shape=(5, 9), extra=["prop1", "prop2"])
-        self.assertEqual(states.prop1.shape, (5, 9))
-        states1 = ct.SolutionArray(self.gas, shape=(0, 0, 0), extra="prop1")
-        self.assertEqual(states1.prop1.shape, (0, 0, 0))
-
-    def test_extra3(self):
-        states2 = ct.SolutionArray(self.gas, shape=(2, 6, 9), extra="prop1")
-        self.assertEqual(states2.prop1.shape, (2, 6, 9))
-
-    def test_extra4(self):
-        states3 = ct.SolutionArray(self.gas, shape=(2, 6, 9), extra=("prop1", "prop2", "prop3"))
-        self.assertEqual(states3.prop3.shape, (2, 6, 9))
-
-    def test_extra5(self):
+    def test_extra_create_by_ndarray(self):
         properties_array = np.array(["prop1", "prop2", "prop3"])
-        states4 = ct.SolutionArray(self.gas, shape=(2, 6, 9), extra=properties_array)
-        self.assertEqual(states4.prop2.shape, (2, 6, 9))
+        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))
+        # Ensure that a 2-dimensional array is flattened
+        properties_array = np.array((["prop1"], ["prop2"]))
+        states = ct.SolutionArray(self.gas, extra=properties_array)
+        self.assertEqual(states.prop1.shape, (0,))
+        self.assertEqual(states.prop2.shape, (0,))
 
     def test_append(self):
         states = ct.SolutionArray(self.gas, 5)
@@ -1766,7 +1763,7 @@ def test_append(self):
 
         self.gas.TPX = 300, 1e4, 'O2:0.5, AR:0.5'
         HPY = self.gas.HPY
-        self.gas.TPX = 1200, 5e5, 'O2:0.3, AR:0.7' # to make sure it gets changed
+        self.gas.TPX = 1200, 5e5, 'O2:0.3, AR:0.7'  # to make sure it gets changed
         states.append(HPY=HPY)
         self.assertEqual(states.cp_mass.shape, (8,))
         self.assertNear(states.P[-1], 1e4)