From 165478b675ae9c94b24967a9f6adc3c68b3924b3 Mon Sep 17 00:00:00 2001
From: Chris McDonough <chrism@plope.com>
Date: Sat, 12 Jun 2010 18:03:00 +0000
Subject: [PATCH] - Make it possible to use ``colander.null`` as a ``missing``
 argument   to ``colander.SchemaNode`` for roundtripping purposes.

- Make it possible to pickle ``colander.null``.
---
 CHANGES.txt          | 11 +++++++++++
 colander/__init__.py | 13 +++++++------
 colander/tests.py    |  7 +++++++
 docs/null.rst        | 15 ++++++++-------
 4 files changed, 33 insertions(+), 13 deletions(-)

diff --git a/CHANGES.txt b/CHANGES.txt
index 293ed5b..3147268 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,6 +1,17 @@
 Changes
 =======
 
+Next Release
+------------
+
+Bug Fixes
+~~~~~~~~~
+
+- Make it possible to use ``colander.null`` as a ``missing`` argument
+  to ``colander.SchemaNode`` for roundtripping purposes.
+
+- Make it possible to pickle ``colander.null``.
+
 0.7.0
 -----
 
diff --git a/colander/__init__.py b/colander/__init__.py
index 8ac6ca3..de6b546 100644
--- a/colander/__init__.py
+++ b/colander/__init__.py
@@ -8,14 +8,16 @@ import translationstring
 
 _ = translationstring.TranslationStringFactory('colander')
 
-class null(object):
+_marker = object()
+
+class _null(object):
     def __nonzero__(self):
         return False
 
     def __repr__(self):
         return '<colander.null>'
 
-null = null()
+null = _null()
 
 def interpolate(msgs):
     for s in msgs:
@@ -1169,7 +1171,7 @@ class SchemaNode(object):
         self.typ = typ
         self.validator = kw.pop('validator', None)
         self.default = kw.pop('default', null)
-        self.missing = kw.pop('missing', null)
+        self.missing = kw.pop('missing', _marker)
         self.name = kw.pop('name', '')
         self.title = kw.pop('title', self.name.capitalize())
         self.description = kw.pop('description', '')
@@ -1194,7 +1196,7 @@ class SchemaNode(object):
         A return value of ``True`` implies that a ``missing`` value
         wasn't specified for this node.  A return value of ``False``
         implies that a ``missing`` value was specified for this node."""
-        return self.missing is null
+        return self.missing is _marker
 
     def serialize(self, appstruct=null):
         """ Serialize the :term:`appstruct` to a :term:`cstruct` based
@@ -1208,7 +1210,6 @@ class SchemaNode(object):
         If an ``appstruct`` argument is not explicitly provided, it
         defaults to :attr:`colander.null`.
         """
-
         if appstruct is null:
             appstruct = self.default
         cstruct = self.typ.serialize(self, appstruct)
@@ -1235,7 +1236,7 @@ class SchemaNode(object):
         """
         if cstruct is null:
             appstruct = self.missing
-            if appstruct is null:
+            if appstruct is _marker:
                 raise Invalid(self, _('Required'))
             # We never deserialize or validate the missing value
             return appstruct
diff --git a/colander/tests.py b/colander/tests.py
index 573eadb..562bf80 100644
--- a/colander/tests.py
+++ b/colander/tests.py
@@ -1340,6 +1340,13 @@ class TestSchemaNode(unittest.TestCase):
         node.missing = 'abc'
         self.assertEqual(node.deserialize(), 'abc')
 
+    def test_deserialize_null_can_be_used_as_missing(self):
+        from colander import null
+        typ = DummyType()
+        node = self._makeOne(typ)
+        node.missing = null
+        self.assertEqual(node.deserialize(null), null)
+
     def test_serialize(self):
         typ = DummyType()
         node = self._makeOne(typ)
diff --git a/docs/null.rst b/docs/null.rst
index 823c0f4..1cd476c 100644
--- a/docs/null.rst
+++ b/docs/null.rst
@@ -255,7 +255,8 @@ an ``age`` key of :attr:`colander.null`, the ``missing`` value of
 
 .. note:: Note that ``None`` can be used for the ``missing`` schema
    node value as required, as in the above example.  It's no different
-   than any other value used as ``missing``.
+   than any other value used as ``missing``.  or ``colander.nuil`` can
+   also be used as the ``missing`` value if that is helpful.
 
 The :attr:`colander.null` value is also the default, so it needn't be
 specified in the cstruct.  Therefore, the ``deserialized`` value of
@@ -287,12 +288,12 @@ Value                 Missing               Result
 ===================== ===================== ===========================
 colander.null         <missing>             Invalid exception raised
 <missing>             <missing>             Invalid exception raised
-colander.null         colander.null         Invalid exception raised
-colander.null         value                 value deserialized
-<missing>             value                 value deserialized
-value                 <missing>             value deserialized
-value                 colander.null         value deserialized
-value_a               value_b               value_a deserialized
+colander.null         value                 value used
+<missing>             value                 value used
+<missing>             colander.null         colander.null used
+value                 <missing>             value used
+value                 colander.null         value used
+value_a               value_b               value_a used
 ===================== ===================== ===========================
 
 .. note:: ``<missing>`` in the above table represents the circumstance