SF bug #461073: mailbox __iter__ bug, by Andrew Dalke.

Andrew quite correctly notices that the next() method isn't quite what
we need, since it returns None upon end instead of raising
StopIteration.  His fix is easy enough, using iter(self.next, None)
instead.

Lib/mailbox.py

@@ -15,7 +15,7 @@ class _Mailbox:
         self.factory = factory
 
     def __iter__(self):
-        return self
+        return iter(self.next, None)
 
     def next(self):
         while 1:
@@ -195,7 +195,7 @@ class MHMailbox:
         self.factory = factory
 
     def __iter__(self):
-        return self
+        return iter(self.next, None)
 
     def next(self):
         if not self.boxes:
@@ -226,7 +226,7 @@ class Maildir:
         self.boxes = boxes
 
     def __iter__(self):
-        return self
+        return iter(self.next, None)
 
     def next(self):
         if not self.boxes: