revert pull 73, add serialize-time drop feature

CHANGES.txt

@@ -4,6 +4,15 @@ Unreleased
 Bug Fixes
 ~~~~~~~~~
 
+- In 1.0a1, there was a change merged from
+  https://github.com/Pylons/colander/pull/73 which made it possible to supply
+  ``None`` as the ``default`` value for a String type, and upon serialization,
+  the value would be rendered as ``colander.null`` if the default were used.
+  This confused people who were actually supplying the value ``None`` as a
+  default when the associated appstruct had no value, so the change has been
+  reverted.  When you supply ``None`` as the ``default`` argument to a String,
+  the rendered serialize() value will again be ``'None'``.  Sorry.
+
 - Normalize ``message`` argument to ``colander.Function`` -> ``msg`` (matches
   other APIs.
 
@@ -17,6 +26,20 @@ Features
 - Add ``colander.List`` type, modeled on ``deform.List``:  this type
   preserves ordering, and allows duplicates.
 
+- It is now possible to use the value ``colander.drop`` as the ``default``
+  value for items that are subitems of a mapping.  If ``colander.drop`` is used
+  as the ``default`` for a subnode of a mapping schema, and the mapping
+  appstruct being serialized does not have a value for that schema node, the
+  value will be omitted from the serialized mapping.  For instance, the
+  following script, when run would not raise an assertion error::
+
+      class What(colander.MappingSchema):
+        thing = colander.SchemaNode(colander.String(), default=colander.drop,
+                                    missing=None)
+
+      result = What().serialize({}) # no "thing" in mapping
+      assert result == {}
+
 1.0a5 (2013-05-31)
 ------------------
 

colander/__init__.py

@@ -545,15 +545,16 @@ class Mapping(SchemaType):
         for num, subnode in enumerate(node.children):
             name = subnode.name
             subval = value.pop(name, null)
-            try:
-                sub_result = callback(subnode, subval)
-            except Invalid as e:
-                if error is None:
-                    error = Invalid(node)
-                error.add(e, num)
-            else:
-                if sub_result is not drop:
-                    result[name] = sub_result
+            if subval is not drop:
+                try:
+                    sub_result = callback(subnode, subval)
+                except Invalid as e:
+                    if error is None:
+                        error = Invalid(node)
+                    error.add(e, num)
+                else:
+                    if sub_result is not drop:
+                        result[name] = sub_result
 
         if self.unknown == 'raise':
             if value:
@@ -1090,7 +1091,7 @@ class String(SchemaType):
         self.encoding = encoding
 
     def serialize(self, node, appstruct):
-        if appstruct in (null, None):
+        if appstruct is null:
             return null
 
         try:
@@ -1136,7 +1137,7 @@ class Number(SchemaType):
     num = None
 
     def serialize(self, node, appstruct):
-        if appstruct in (null, None):
+        if appstruct is null:
             return null
 
         try:

colander/tests/test_colander.py

@@ -653,6 +653,14 @@ class TestMapping(unittest.TestCase):
         result = typ.serialize(node, null)
         self.assertEqual(result, {'a':null})
 
+    def test_serialize_value_has_drop(self):
+        from colander import drop
+        node = DummySchemaNode(None)
+        node.children = [DummySchemaNode(None, name='a')]
+        typ = self._makeOne()
+        result = typ.serialize(node, {'a':drop})
+        self.assertEqual(result, {})
+        
     def test_flatten(self):
         node = DummySchemaNode(None, name='node')
         int1 = DummyType()
@@ -1350,14 +1358,6 @@ class TestString(unittest.TestCase):
         result = typ.serialize(node, null)
         self.assertEqual(result, null)
 
-    def test_serialize_none(self):
-        import colander
-        val = None
-        node = DummySchemaNode(None)
-        typ = self._makeOne()
-        result = typ.serialize(node, val)
-        self.assertEqual(result, colander.null)
-
     def test_serialize_emptystring(self):
         val = ''
         node = DummySchemaNode(None)
@@ -1427,14 +1427,6 @@ class TestInteger(unittest.TestCase):
         result = typ.serialize(node, val)
         self.assertEqual(result, colander.null)
 
-    def test_serialize_none(self):
-        import colander
-        val = None
-        node = DummySchemaNode(None)
-        typ = self._makeOne()
-        result = typ.serialize(node, val)
-        self.assertEqual(result, colander.null)
-
     def test_serialize_emptystring(self):
         import colander
         val = ''