simplify metaclass logic, punt on trying to divine intent in multiple inheritance case

colander/__init__.py

@@ -1917,6 +1917,7 @@ class _SchemaNode(object):
 class _SchemaMeta(type):
     def __init__(cls, name, bases, clsattrs):
         nodes = []
+
         for name, value in clsattrs.items():
             if isinstance(value, _SchemaNode):
                 delattr(cls, name)
@@ -1925,16 +1926,15 @@ class _SchemaMeta(type):
                 if value.raw_title is _marker:
                     value.title = name.replace('_', ' ').title()
                 nodes.append((value._order, value))
-        cls.__class_schema_nodes__ = nodes
-        # Combine all attrs from this class and its subclasses.
-        extended = []
-        for i, c in enumerate(reversed(cls.__mro__)):
+
+        nodes.sort()
+        cls.__class_schema_nodes__ = [ n[1] for n in nodes ]
+
+        # Combine all attrs from this class and its _SchemaNode superclasses.
+        cls.__all_schema_nodes__ = []
+        for c in reversed(cls.__mro__):
             csn = getattr(c, '__class_schema_nodes__', [])
-            extended.extend([(i, x, y) for x, y in csn])
-        # Sort the attrs to maintain the order as defined, and assign to the
-        # class.
-        extended.sort()
-        cls.__all_schema_nodes__ = [x[2] for x in extended]
+            cls.__all_schema_nodes__.extend(csn)
 
 # metaclass spelling compatibility across Python 2 and Python 3
 SchemaNode = _SchemaMeta(

colander/tests/test_colander.py

@@ -2631,6 +2631,56 @@ class TestMappingSchemaInheritance(unittest.TestCase):
              ]
             )
 
+    def test_single_inheritance2(self):
+        import colander
+        class One(colander.Schema):
+            a = colander.SchemaNode(
+                colander.Int(),
+                id='a1',
+                )
+            b = colander.SchemaNode(
+                colander.Int(),
+                id='b1',
+                )
+            d = colander.SchemaNode(
+                colander.Int(),
+                id='d1',
+                )
+
+        class Two(One):
+            a = colander.SchemaNode(
+                colander.String(),
+                id='a2',
+                )
+            c = colander.SchemaNode(
+                colander.String(), 
+                id='c2',
+                )
+            e = colander.SchemaNode(
+                colander.String(),
+                id='e2',
+                )
+            
+        class Three(Two):
+            b = colander.SchemaNode(
+                colander.Bool(),
+                id='b3',
+                )
+            d = colander.SchemaNode(
+                colander.Bool(),
+                id='d3',
+                )
+            f = colander.SchemaNode(
+                colander.Bool(),
+                id='f3',
+                )
+
+        inst = Three()
+        c = inst.children
+        self.assertEqual(len(c), 6)
+        result = [ x.id for x in c ]
+        self.assertEqual(result, ['a2', 'b3', 'd3', 'c2', 'e2', 'f3'])
+
     def test_multiple_inheritance(self):
         import colander
         class One(colander.Schema):
@@ -2661,7 +2711,7 @@ class TestMappingSchemaInheritance(unittest.TestCase):
                 id='e2',
                 )
             
-        class Three(One, Two):
+        class Three(Two, One):
             b = colander.SchemaNode(
                 colander.Bool(),
                 id='b3',
@@ -2676,13 +2726,10 @@ class TestMappingSchemaInheritance(unittest.TestCase):
                 )
 
         inst = Three()
-        self.assertEqual(len(inst.children), 6)
-        self.assertEqual(inst.children[0].id, 'a1')
-        self.assertEqual(inst.children[1].id, 'b3')
-        self.assertEqual(inst.children[2].id, 'd3')
-        self.assertEqual(inst.children[3].id, 'c2')
-        self.assertEqual(inst.children[4].id, 'e2')
-        self.assertEqual(inst.children[5].id, 'f3')
+        c = inst.children
+        self.assertEqual(len(c), 6)
+        result = [ x.id for x in c ]
+        self.assertEqual(result, ['a2', 'b3', 'd3', 'c2', 'e2', 'f3'])
 
     def test_insert_before_failure(self):
         import colander