Pay attention to copy_reg

Fixes the pickling of zope.securitypolicy.settings.{Allow,Deny,Unset},
makes zopefoundation/zope.securitypolicy#1
unnecessary.

src/mongopersist/serialize.py

@@ -149,7 +149,12 @@ def get_non_persistent_state(self, obj, seen):
                 getattr(obj, '_m_reference_safe', False)):
             seen.append(id(obj))
         # Get the state of the object. Only pickable objects can be reduced.
-        reduced = obj.__reduce__()
+        reduce_fn = copy_reg.dispatch_table.get(type(obj))
+        if reduce_fn is not None:
+            reduced = reduce_fn(obj)
+        else:
+            # XXX: __reduce_ex__
+            reduced = obj.__reduce__()
         # The full object state (item 3) seems to be optional, so let's make
         # sure we handle that case gracefully.
         if isinstance(reduced, str):

src/mongopersist/tests/test_serialize.py

@@ -16,6 +16,7 @@
 import doctest
 import persistent
 import pprint
+import copy_reg
 
 from bson import binary, dbref, objectid
 
@@ -60,6 +61,12 @@ def __reduce__(self):
         return 'Constant'
 Constant = Constant()
 
+class CopyReggedConstant(object):
+    def custom_reduce_fn(self):
+        return 'CopyReggedConstant'
+copy_reg.pickle(CopyReggedConstant, CopyReggedConstant.custom_reduce_fn)
+CopyReggedConstant = CopyReggedConstant()
+
 
 def doctest_ObjectSerializer():
     """Test the abstract ObjectSerializer class.
@@ -328,6 +335,8 @@ def doctest_ObjectWriter_get_state_constant():
       {'_py_constant': 'mongopersist.tests.test_serialize.Constant'}
       >>> writer.get_state(interfaces.IObjectWriter)
       {'_py_constant': 'mongopersist.interfaces.IObjectWriter'}
+      >>> writer.get_state(CopyReggedConstant)
+      {'_py_constant': 'mongopersist.tests.test_serialize.CopyReggedConstant'}
     """
 
 def doctest_ObjectWriter_get_state_types():