--- a/treepkg/status.py	Thu Mar 15 12:20:12 2007 +0100
+++ b/treepkg/status.py	Thu Mar 15 13:00:01 2007 +0100
@@ -51,8 +51,24 @@
         return datetime.datetime(*time.strptime(string.strip(),
                                                 self.date_format)[:6])
 
+class StatusMetaClass(type):
+
+    def __new__(cls, name, bases, clsdict):
+        # Generate the _fields class variable from the field descriptors
+        # in clsdict.
+        fields = dict()
+        for key, value in clsdict.items():
+            if isinstance(value, FieldDesc):
+                fields[key] = value
+                del clsdict[key]
+        clsdict["_fields"] = fields
+        return type.__new__(cls, name, bases, clsdict)
+
+
 class Status(object):
 
+    __metaclass__ = StatusMetaClass
+
     # Overwrite in derived classes with a different magic string
     _magic = "Status 0.0\n"
 
@@ -60,10 +76,6 @@
     # variables.
     _attrs = set(["_filename", "_values"])
 
-    # Derived classes should set this to a suitable list of attribute
-    # descriptors
-    _fields = ()
-
     def __init__(self, filename):
         assert os.path.isabs(filename)
         self._filename = filename
@@ -118,7 +130,6 @@
 
     _magic = "TreePackagerStatus 0.0\n"
 
-    _fields = dict(status=StringFieldDesc(default="unknown"),
-                   start=DateFieldDesc(default=None),
-                   stop=DateFieldDesc(default=None))
-
+    status = StringFieldDesc(default="unknown")
+    start = DateFieldDesc(default=None)
+    stop = DateFieldDesc(default=None)