I have MIME message and parse content. Later I walk on message headers by call for and receive follow traceback:

Traceback (most recent call last):
...
    for m in msg:  (msg is email.message.Message instance)
  File "C:\Python27\lib\email\message.py", line 294, in __getitem__
    return self.get(name)
  File "C:\Python27\lib\email\message.py", line 360, in get
    name = name.lower()
AttributeError: 'int' object has no attribute 'lower'

But with items() all work properly.