##
12.10.2 `MultiFile` の例

    import mimetools
    import multifile
    import StringIO

    def extract_mime_part_matching(stream, mimetype):
        """Return the first element in a multipart MIME message on stream
        matching mimetype."""

        msg = mimetools.Message(stream)
        msgtype = msg.gettype()
        params = msg.getplist()

        data = StringIO.StringIO()
        if msgtype[:10] == "multipart/":

            file = multifile.MultiFile(stream)
            file.push(msg.getparam("boundary"))
            while file.next():
                submsg = mimetools.Message(file)
                try:
                    data = StringIO.StringIO()
                    mimetools.decode(file, data, submsg.getencoding())
                except ValueError:
                    continue
                if submsg.gettype() == mimetype:
                    break
            file.pop()
        return data.getvalue()