Undocumented feature: MHMailbox sets the msg object's _mh_msgno

attribute to the (stringized) message number (if this attribute is
settable).  This is useful so users of this class can report the
correct message number (e.g. when classifying spam).

Also added a blank line before the first method of each class.

Lib/mailbox.py

@@ -10,6 +10,7 @@ __all__ = ["UnixMailbox","MmdfMailbox","MHMailbox","Maildir","BabylMailbox",
            "PortableUnixMailbox"]
 
 class _Mailbox:
+
     def __init__(self, fp, factory=rfc822.Message):
         self.fp = fp
         self.seekp = 0
@@ -35,6 +36,7 @@ class _Mailbox:
 
 
 class _Subfile:
+
     def __init__(self, fp, start, stop):
         self.fp = fp
         self.start = start
@@ -94,6 +96,7 @@ class _Subfile:
 
 # Recommended to use PortableUnixMailbox instead!
 class UnixMailbox(_Mailbox):
+
     def _search_start(self):
         while 1:
             pos = self.fp.tell()
@@ -161,6 +164,7 @@ class PortableUnixMailbox(UnixMailbox):
 
 
 class MmdfMailbox(_Mailbox):
+
     def _search_start(self):
         while 1:
             line = self.fp.readline()
@@ -181,6 +185,7 @@ class MmdfMailbox(_Mailbox):
 
 
 class MHMailbox:
+
     def __init__(self, dirname, factory=rfc822.Message):
         import re
         pat = re.compile('^[1-9][0-9]*$')
@@ -204,7 +209,12 @@ class MHMailbox:
             return None
         fn = self.boxes.pop(0)
         fp = open(os.path.join(self.dirname, fn))
-        return self.factory(fp)
+        msg = self.factory(fp)
+        try:
+            msg._mh_msgno = fn
+        except (AttributeError, TypeError):
+            pass
+        return msg
 
 
 class Maildir:
@@ -238,6 +248,7 @@ class Maildir:
 
 
 class BabylMailbox(_Mailbox):
+
     def _search_start(self):
         while 1:
             line = self.fp.readline()