here is my code
@api.multi
def modification_approval(self):
attend_signin_ids = self.env['hr.attendance'].search([('employee_id','=',self.employee_id.id)])
check_in_date = datetime.datetime.strptime(self.time_check_in_1, "%y-%m-%d %H:%M:%S").date()
check_out_date = datetime.datetime.strptime(self.time_check_out_1, "%y-%m-%d %H:%M:%S").date()
for obj in attend_signin_ids:
attendance_check_in_date = datetime.datetime.strptime(obj.check_in, "%y-%m-%d %H:%M:%S").date()
attendance_check_out_date = datetime.datetime.strptime(obj.check_out, "%y-%m-%d %H:%M:%S").date()