Email Openerp向多个收件人发送电子邮件

我正在使用模板发送电子邮件。我想将电子邮件发送给多个收件人，但在字段email_中，仅接受对象属性：

<field name="email_to">${object.attribute}</field>

def action_send_email_to_attendees(self, cr, uid, ids, context=None):
        '''
        This function opens a window to compose an email
        '''
        assert len(ids) == 1, 'This option should only be used for a single id at a time.'
        ir_model_data = self.pool.get('ir.model.data')
        try:
            template_id = ir_model_data.get_object_reference(cr, uid, 'mymodule', 'mymodule_invitation_email')[1]
        except ValueError:
            template_id = False
        try:
            compose_form_id = ir_model_data.get_object_reference(cr, uid, 'mail', 'email_compose_message_wizard_form')[1]
        except ValueError:
            compose_form_id = False 
        ctx = dict(context)
        ctx.update({
            'default_model': 'mymodule.module',
            'default_res_id': ids[0],
            'default_use_template': bool(template_id),
            'default_template_id': template_id,
            'default_composition_mode': 'comment',
            'mark_so_as_sent': True
        })
        return {
            'type': 'ir.actions.act_window',
            'view_type': 'form',
            'view_mode': 'form',
            'res_model': 'mail.compose.message',
            'views': [(compose_form_id, 'form')],
            'view_id': compose_form_id,
            'target': 'new',
            'context': ctx,
        }