code: def cancel_order(self, order_id):
          
          self._log('cancel order {}'.format(order_id))
          result = self._rest_client.post(
              endpoint='/cancel_order',
              payload={'id': order_id}
          )
          return result == 'true'
docs: Cancel an open order by ID (64 hexadecmial characters).
  
          :param order_id: Order ID.
          :type order_id: str | unicode
          :return: True if the order was cancelled successfully.
          :rtype: bool