''

def cancelOrder(self, instrument, orderID, frontID, sessionID):

    self.reqID += 1
    req = {}
    req['InstrumentID'] = instrument
    req['OrderRef'] = orderID
    req['FrontID'] = frontID
    req['SessionID'] = sessionID
    req['ActionFlag'] = defineDict['THOST_FTDC_AF_Delete']
    req['BrokerID'] = self.brokerID
    req['InvestorID'] = self.userID
    self.reqOrderAction(req, self.reqID)
