'Create a message/* type MIME document.
_msg is a message object and must be an instance of Message, or a
derived class of Message, otherwise a TypeError is raised.
Optional _subtype defines the subtype of the contained message.  The
default is "rfc822" (this is defined by the MIME standard, even though
the term "rfc822" is technically outdated by RFC 2822).'

def __init__(self, _msg, _subtype='rfc822'):

    MIMENonMultipart.__init__(self, 'message', _subtype)
    if (not isinstance(_msg, message.Message)):
        raise TypeError('Argument    is    not    an    instance    of    Message')
    message.Message.attach(self, _msg)
    self.set_default_type('message/rfc822')
