Interactive Brokers Python API Connection buffer

Question

I am trying to develop a stock screener for screening price action at a specific time frame on multiple stocks. Hence, I will need to automate pulling data from IB on multiple instruments with sufficient memory buffer.

The server can be connected smoothly if I only run the script once.

TWS Time at connection:20171206 12:00:11 CST

After successful connection, I used ibpy to pull out historical data. The data was downloaded successfully with no problems. However, when I try to pull data from same instrument with the same settings again.

TWS Time at connection:20171206 12:00:11 CST
Server Error: <error id=None, errorCode=None, errorMsg=unpack requires a buffer of 1 bytes>

I am not sure how to allocate memory buffer for performing this task. I am a newbie in Python and no knowledge in buffer allocation. Please advise in super simple language on solving the server error. Thank you in advance for the help and effort!! (Ideally, there is no need to go deeper into editing the ibpy core codes for my easier understanding)

I tried to contact IB customer service for API support but in vain due to lack of error code.

Here are codes related to the connection of IB.

def connect_to_tws(self):
    self.tws_conn = Connection.create(port=7497, clientId=5)
    self.tws_conn.connect()
    self.register_callback_functions()

def contract_creation(self):
    self.listbox1.delete(0,END) # clears contents of the listbox
    self.tws_conn.cancelHistoricalData(5) #cancels historical data
    mySymbol = self.input.symbol # get the symbol from the combobox

    contract = self.create_contract(mySymbol,
                               'STK',   # security STK = stock 
                               'SEHK', # exchange
                               '',# primary exchange
                               'HKD')   # currency

    duration = self.input.duration # get the duration ie. 1 D, 1 M, 1 Y
    bar_size = self.input.barsize  # get the bar size ie. 5 mins, 2 mins, 1 day

    self.tws_conn.reqHistoricalData(tickerId = 5,       # contract number can be any number
                                    contract=contract,  # contract detail from about
                                    endDateTime=self.input.now,    # end date and time
                                    durationStr=duration,    
                                    barSizeSetting=bar_size,
                                    whatToShow='TRADES', # what to show ie. MIDPOINT, BID, ASK,
                                    useRTH=1,          # Regular trading hours 1 = RTH, 0 = all data
                                    formatDate=1)   # 1 = 20161021  09:30:00 2 = Unix time (Epoch)

def register_callback_functions(self):
    # Assign server messages handling function.
    self.tws_conn.registerAll(self.server_handler)

    # Assign error handling function.
    self.tws_conn.register(self.error_handler, 'Error')

def error_handler(self, msg):
    if msg.typeName == 'error'and msg.id != -1:
        print ('Server Error:', msg)

def server_handler(self, msg):    
    if msg.typeName == 'historicalData':
        hd_date = msg.date
        hd_open = msg.open
        hd_high = msg.high
        hd_low = msg.low
        hd_close = msg.close
        hd_volume = msg.volume

        str_date = str(hd_date)
        str_open = str(hd_open)
        str_high = str(hd_high)
        str_low = str(hd_low)
        str_close = str(hd_close)
        str_volume = str(hd_volume)
        # creates a string containing date, open, high, low, close, volume
        priceData2 = hd_date+","+str_open+","+str_high+","+str_low+","+str_close+","+str_volume

        if 'finished' in hd_date:
            pass
        else:
            str_data = hd_date, hd_open, hd_high, hd_low, hd_close, hd_volume
            print (str_data) # prints info to the Python shell
            self.listbox1.insert(END, priceData2) # adds info to the listbox

    elif msg.typeName == "error" and msg.id != -1:
        return

def create_contract(self, symbol, sec_type, exch, prim_exch, curr):
    contract = Contract()
    contract.m_symbol = symbol
    contract.m_secType = sec_type
    contract.m_exchange = exch
    contract.m_primaryExch = prim_exch
    contract.m_currency = curr
    return contract        

Answer 1

I'm working with the IBpy-library every day and I never had problems with the buffer size. Maybe you'll tell us more about your environment (OS, CPU, RAM)? Did other examples with IBpy work?

The communication with IB isn't easy but with putting some print("Line xx works")you will know where the error occurs and by sending more concrete information to IB by message they'll help you friendly.