save_zip.py

    @api.one
    def add_attachment(self, content):
        """
        TODO
        """
        buf = StringIO() # from io import StringIO
        buf.write(content)
        document = base64.encodebytes(buf.getvalue().encode())
        buf.close()
        attach = self.env["ir.attachment"].create(
            {
                "name": "nombre.zip",
                "datas": document,
                "datas_fname": "nombre.zip",
                # "res_model": self._name,
                # "res_id": self.id,
                "type": "binary",
            }
        )
        return attach