On Windows, mimetypes initialization reads the list of MIME types from the Windows registry. It assumes that all characters are Latin-1 encoded, and fails when it's not the case, with the following exception:

Traceback (most recent call last):
  File "mttest.py", line 3, in <module>
    mimetypes.init()
  File "c:\Python27\lib\mimetypes.py", line 355, in init
    db.read_windows_registry()
  File "c:\Python27\lib\mimetypes.py", line 260, in read_windows_registry
    for ctype in enum_types(mimedb):
  File "c:\Python27\lib\mimetypes.py", line 250, in enum_types
    ctype = ctype.encode(default_encoding) # omit in 3.x!
UnicodeDecodeError: 'ascii' codec can't decode byte 0xe0 in position 0: ordinal not in range(128)

This can be reproduced, for example, on a Russian Windows XP installation which has QuickTime installed (QuickTime creates the non-Latin entries in the registry). The following line causes the exception to happen:

import mimetypes; mimetypes.init()