When saving a source file with non-ascii characters from an IDLE window,
on Windows platform (XP and Server 2003 at least)
with locale English US  

  locale.getdefaultlocale()
  ('en_US', 'cp1252')

IDLE prompts in IOBinding.py with the message 
"non Ascii found, yet no encoding declared, Add a line like # -*- 
coding: cp1252 -*-"

If accepted, the file is saved with the wrong encoding.
Afterwards, it is read back by IDLE without any problem and it looks 
good in the IDLE window.

However, if a string with non-ascii characters is sent to another 
module (i.e. email  MIMEText)
the string is wrong.

The same source would be rejected by python in terminal mode and by 
IDLE on Linux.