Interactive brokers native API. - problem with client. disconnect()

Question

I am a noob programmer without a computer science background. I learned to code by trial and error and with online help.

I wrote the following code to download hourly candles from IB TWS. There is a problem with client.disconnet(). This causes "Error Code: 504 & Error Message: Not connected". If I remove this line -client.disconnect() from the code and run it again, the error message disappears but API connection stays active. API connection staying active is ok but it seems inefficient way of doing it.

How can it overcome this error message Thanks

Here is the full code and error message

from ibapi.client import EClient, Contract
from ibapi.wrapper import EWrapper
from ibapi.utils import iswrapper
import datetime
from datetime import date 
from datetime import time
from threading import Thread
import time
import socket
import pandas as pd
import talib as ta
import os




class ReadTicker(EWrapper, EClient):
    ''' Serves as the client and the wrapper '''

    def __init__(self, addr, port, client_id):
        EClient.__init__(self, self)

        # Initialize properties
        self.usdpair = {'AUD':'14433401', 'EUR':'12087792', 'GBP':'12087797'}
                              
        self.candle_dict = {}

        # Connect to TWS
        self.connect('127.0.0.1', 7497, 304)

        # Launch the client thread
        thread = Thread(target=self.run)
        thread.start()
        
 
    @iswrapper
    def historicalData(self, req_id, bar):
        ''' Callback to reqHistoricalData '''

        # Add the instrument prices to the dictionary
        self.candle_dict['Date'].append(bar.date)
        self.candle_dict['Open'].append(bar.open)
        self.candle_dict['High'].append(bar.high)
        self.candle_dict['Low'].append(bar.low)
        self.candle_dict['Close'].append(bar.close)
    
    def error(self, req_id, code, msg):
        print('Error Code: {} & Error Message: {}'.format(code, msg))


    def main():
        start = datetime.time(9, 0, 0)
        end = datetime.time(22, 0, 0)
        current = datetime.datetime.now().time()
        if start <= current <= end:
            # Make directory for csv file n create path
            if not os.path.exists(r'C:\TWSAPI\samples\Python\Testbed\xlsfiles'):
                os.makedirs(r'C:\TWSAPI\samples\Python\Testbed\xlsfiles')
            root = r'C:\TWSAPI\samples\Python\Testbed\xlsfiles'

        
        #Create the client and connect to TWS 
        client = ReadTicker('127.0.0.1', 7497, 304)
        time.sleep(10) #Sleep interval to allow time for connection to server
    

        reqId = 2001
        for usdpair in client.usdpair:
            # Define the contract
            usdcontract = Contract()
            usdcontract.symbol = usdpair
            usdcontract.secType = 'CASH'
            usdcontract.exchange = 'IDEALPRO'
            usdcontract.currency = "USD"
            usdcontract.conId = client.usdpair[usdpair]
            print('OHLC Data download for {}USD started.'.format(usdpair)) 
            for v in ['Date','Open', 'High', 'Low', 'Close']: 
                client.candle_dict[v] = []

            now = datetime.datetime.now().strftime("%Y%m%d %H:%M:%S")
            client.reqHistoricalData(reqId, usdcontract, now, '7 D', '1 hour', 'TRADES', False, 1, False, [])
            reqId += 1
            time.sleep(5) 
            df = pd.DataFrame(client.candle_dict, columns=['Date', 'Open', 'High', 'Low', 'Close'])
            df['Date'] = pd.to_datetime(df['Date']) 
                        
            df.to_csv(root + '/'+ usdpair + 'USD' + '.csv', encoding='utf-8', index= False)
            client.candle_dict.clear()
        
            client.disconnect()

    else:
        print('Trading time is over')
    
    
if __name__ == '__main__':
    main()

Error Message: is as follows:

Error Code: 2104 & Error Message: Market data farm connection is OK:uscrypto
Error Code: 2104 & Error Message: Market data farm connection is OK:usfarm.nj
Error Code: 2104 & Error Message: Market data farm connection is OK:hfarm
Error Code: 2104 & Error Message: Market data farm connection is OK:cashfarm
Error Code: 2106 & Error Message: HMDS data farm connection is OK:euhmds
Error Code: 2106 & Error Message: HMDS data farm connection is OK:cashhmds
Error Code: 2106 & Error Message: HMDS data farm connection is OK:hkhmds
Error Code: 2106 & Error Message: HMDS data farm connection is OK:fundfarm
Error Code: 2106 & Error Message: HMDS data farm connection is OK:ushmds
Error Code: 2158 & Error Message: Sec-def data farm connection is OK:secdefhk
OHLC Data download for AUDUSD started.
Error Code: 162 & Error Message: Historical Market Data Service error message:No historical market data for AUD/CASH@FXSUBPIP Last 3600
OHLC Data download for EURUSD started.
Error Code: 504 & Error Message: Not connected
unhandled exception in EReader thread
Traceback (most recent call last):
  File "C:\Users\venky\anaconda3\lib\site-packages\ibapi-9.76.1-py3.8.egg\ibapi\reader.py", line 34, in run
    data = self.conn.recvMsg()
  File "C:\Users\venky\anaconda3\lib\site-packages\ibapi-9.76.1-py3.8.egg\ibapi\connection.py", line 99, in recvMsg
    buf = self._recvAllMsg()
  File "C:\Users\venky\anaconda3\lib\site-packages\ibapi-9.76.1-py3.8.egg\ibapi\connection.py", line 119, in _recvAllMsg
    buf = self.socket.recv(4096)
OSError: [WinError 10038] An operation was attempted on something that is not a socket
OHLC Data download for GBPUSD started.
Error Code: 504 & Error Message: Not connected
PS C:\TWSAPI\samples\Python\Testbed>