Make deleting '_p_oid' in Python Persistent work like C too.

CHANGES.rst

@@ -4,9 +4,9 @@
 4.0.8 (Unreleased)
 ------------------
 
-- Make it possible to delete the ``_p_jar`` of a pure-Python
-  ``Persistent`` object (fixes aborting a ZODB Connection that
-  has added objects).
+- 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)
 
 4.0.7 (2014-02-20)
 ------------------

persistent/persistence.py

@@ -98,8 +98,11 @@ class Persistent(object):
         self.__oid = value
 
     def _del_oid(self):
-        if self.__jar is not None:
-            raise ValueError('Cannot delete OID once assigned to a jar')
+        jar = self.__jar
+        oid = self.__oid
+        if jar is not None:
+            if oid and jar._cache.get(oid):
+                raise ValueError('Cannot delete _p_oid of cached object')
         self.__oid = None
 
     _p_oid = property(_get_oid, _set_oid, _del_oid)

persistent/tests/test_persistence.py

@@ -86,23 +86,20 @@ class _Persistent_Base(object):
         self.assertEqual(inst._p_sticky, False)
         self.assertEqual(inst._p_status, 'unsaved')
 
-    def test_cannot_del_jar_while_in_cache(self):
+    def test_del_jar_while_in_cache(self):
         inst, _, OID = self._makeOneWithJar()
         def _test():
             del inst._p_jar
         self.assertRaises(ValueError, _test)
 
-    def test_del_jar_oid_like_ZODB_abort(self):
-        # When a ZODB connection aborts,
-		# it removes registered objects from the cache,
-		# deletes their jar, deletes their OID
-		# and finally sets p_changed to false
+    def test_del_jar_like_ZODB_abort(self):
+        # When a ZODB connection aborts, it removes registered objects from
+        # the cache, deletes their jar, deletes their OID, and finally sets
+        # p_changed to false
         inst, jar, OID = self._makeOneWithJar()
         del jar._cache[OID]
         del inst._p_jar
         self.assertEqual(inst._p_jar, None)
-        del inst._p_oid
-        self.assertEqual(inst._p_oid, None)
 
     def test_assign_p_jar_w_new_jar(self):
         inst, jar, OID = self._makeOneWithJar()
@@ -164,6 +161,15 @@ class _Persistent_Base(object):
             del inst._p_oid
         self.assertRaises(ValueError, _test)
 
+    def test_del_oid_like_ZODB_abort(self):
+        # When a ZODB connection aborts, it removes registered objects from
+        # the cache, deletes their jar, deletes their OID, and finally sets
+        # p_changed to false
+        inst, jar, OID = self._makeOneWithJar()
+        del jar._cache[OID]
+        del inst._p_oid
+        self.assertEqual(inst._p_oid, None)
+
     def test_assign_p_serial_w_invalid_type(self):
         inst = self._makeOne()
         def _test():