Addressing corner cases for datastore.Key.__eq__.

These corners are a direct result of #274.

gcloud/datastore/key.py

@@ -256,9 +256,24 @@ def __eq__(self, other):
         if self is other:
             return True
 
-        return (self._dataset_id == other._dataset_id and
-                self.namespace() == other.namespace() and
-                self.path() == other.path())
+        if not isinstance(other, self.__class__):
+            return False
+
+        # Check that paths match.
+        if self.path() != other.path():
+            return False
+
+        # Check that datasets match.
+        if not (self._dataset_id == other._dataset_id or
+                self._dataset_id is None or other._dataset_id is None):
+            return False
+
+        # Check that namespaces match.
+        if not (self._namespace == other._namespace or
+                self._namespace is None or other._namespace is None):
+            return False
+
+        return True
 
     def __ne__(self, other):
         return not self.__eq__(other)

gcloud/datastore/test_key.py

@@ -332,3 +332,21 @@ def test_key___eq__(self):
         self.assertEqual(key1, key1)
         key3 = self._getTargetClass().from_path('abc', 'ghi')
         self.assertNotEqual(key1, key3)
+
+    def test_key___eq___wrong_type(self):
+        key = self._getTargetClass().from_path('abc', 'def')
+        self.assertNotEqual(key, 10)
+
+    def test_key___eq___dataset_id(self):
+        key1 = self._getTargetClass().from_path('abc', 'def')
+        key2 = self._getTargetClass().from_path('abc', 'def', dataset_id='foo')
+        self.assertEqual(key1, key2)
+        key3 = self._getTargetClass().from_path('abc', 'def', dataset_id='bar')
+        self.assertNotEqual(key2, key3)
+
+    def test_key___eq___namespace(self):
+        key1 = self._getTargetClass().from_path('abc', 'def')
+        key2 = self._getTargetClass().from_path('abc', 'def', namespace='foo')
+        self.assertEqual(key1, key2)
+        key3 = self._getTargetClass().from_path('abc', 'def', namespace='bar')
+        self.assertNotEqual(key2, key3)