except TopLevelLookupException:

                    pass

    def normalize_attachments(self, attachments):

        normalized = []

        for attachment in attachments:

            if isinstance(attachment, six.string_types):

                attachment = self.normalize_attachment(attachment)

            normalized.append(attachment)

        return normalized

    ATTACHMENT_MIME_MAP = {

        '.pdf': 'pdf',

        '.xls': 'vnd.ms-excel',

    }

    def normalize_attachment(self, path):

        root, ext = os.path.splitext(path)

        ext = ext.lower()

        if ext == '.csv':

            with open(path, 'rb') as f:

                part = MIMEText(f.read(), 'csv', 'utf_8')

            filename = os.path.basename(path)

            part.add_header('Content-Disposition', 'attachment; filename="{}"'.format(filename))