The pure-Python Persistent class no longer calls subclass's __setattr__ at...

The pure-Python Persistent class no longer calls subclass's __setattr__ at instance creation time, just like the C version.

CHANGES.rst

@@ -4,6 +4,9 @@
 4.0.8 (Unreleased)
 ------------------
 
+- The pure-Python ``Persistent`` class no longer calls subclass's
+  ``__setattr__`` at instance creation time. (PR #8)
+
 - Make it possible to delete ``_p_jar`` / ``_p_oid`` of a pure-Python
   ``Persistent`` object which has been removed from the jar's cache
   (fixes aborting a ZODB Connection that has added objects). (PR #7)

persistent/persistence.py

@@ -53,11 +53,15 @@ class Persistent(object):
 
     def __new__(cls, *args, **kw):
         inst = super(Persistent, cls).__new__(cls)
-        inst.__jar = None
-        inst.__oid = None
-        inst.__serial = None
-        inst.__flags = None
-        inst.__size = 0
+        # We bypass the __setattr__ implementation of this object
+        # at __new__ time, just like the C implementation does. This
+        # makes us compatible with subclasses that want to access
+        # properties like _p_changed in their setattr implementation
+        _OSA(inst, '_Persistent__jar', None)
+        _OSA(inst, '_Persistent__oid', None)
+        _OSA(inst, '_Persistent__serial', None)
+        _OSA(inst, '_Persistent__flags', None)
+        _OSA(inst, '_Persistent__size', 0)
         return inst
 
     # _p_jar:  see IPersistent.

persistent/tests/test_persistence.py

@@ -1325,6 +1325,14 @@ class _Persistent_Base(object):
         class mixed2(self._getTargetClass(), alternate):
             pass
 
+    def test_setattr_in_subclass_is_not_called_creating_an_instance(self):
+        class subclass(self._getTargetClass()):
+            _v_setattr_called = False
+            def __setattr__(self, name, value):
+                object.__setattr__(self, '_v_setattr_called', True)
+                super(subclass,self).__setattr__(name, value)
+        inst = subclass()
+        self.assertEqual(object.__getattribute__(inst,'_v_setattr_called'), False)
 
 class PyPersistentTests(unittest.TestCase, _Persistent_Base):