How to declare a global variable of pySerial with Python

Question

Using Python I need to call the 'configSerialPort' function several times and for that I have declared serialPort as global and it is my code:

import serial

comPort = 'COM5'
serialPort = None

def configSerialPort(timeout):
   serialPort = serial.Serial(port = comPort, baudrate = 9600, timeout = timeout)

def ping():
   #serialPort = serial.Serial(port = comPort, baudrate = 9600, timeout = 1)
   command = "AT\n"
   serialPort.write(command.encode('ASCII'))
   bufferRxSerial = serialPort.readline().decode('ASCII')
   if( bufferRxSerial.strip() == "OK" ):
       return True
   else:
       return False


def main():
   global serialPort
   configSerialPort(3)
   flagConexion = ping()
   if flagConexion == True:
       print('The Modem is connected!')
   else:
       print('ERROR, no connection to modem!')

main()

but I have this error:

File "C:/Users/WSR/AppData/Local/Programs/Python/Python39/TestSerialPort.py", line 12, in ping
serialPort.write(command.encode('ASCII'))
AttributeError: 'NoneType' object has no attribute 'write'

how can I correct it

Answer 1

Whenever you want to access a global variable in a function, you should declare it as global

def configSerialPort(timeout):
   global serialPort
   ...
def ping():
   global serialPort
   ...