--- a/treepkg/status.py	Thu Sep 09 13:49:37 2010 +0000
+++ b/treepkg/status.py	Thu Sep 09 14:26:35 2010 +0000
@@ -121,11 +121,12 @@
 
     # Derived classes may extend a copy of this set with more instance
     # variables.
-    _attrs = set(["_filename", "_values"])
+    _attrs = set(["_filename", "_values", "_after_setattr"])
 
-    def __init__(self, filename):
+    def __init__(self, filename, after_setattr=None):
         self._values = dict()
         self._filename = filename
+        self._after_setattr = after_setattr
         if self._filename is not None:
             assert os.path.isabs(self._filename)
             self.read()
@@ -178,6 +179,8 @@
         if attr in self._fields:
             self._values[attr] = value
             self.write()
+            if self._after_setattr is not None:
+                self._after_setattr(self, attr)
         elif attr in self._attrs:
             self.__dict__[attr] = value
         else: