uarttest.py

#!/bin/usr/python

import os; windows = os.name == "nt"
import sys
import serial
import threading
import time

comPort = None

def TransmitThread():
  while comPort:
    for n in range(ord("A"),ord("Z")+1):
      if comPort:
        comPort.write(chr(n).encode())
        time.sleep(1)

def ReceiveThread():
  while comPort:
    if comPort.inWaiting() > 0:
      n = comPort.read(1)
      print(chr(ord(n)))
    else:
      time.sleep(0.1)

def LoopbackTest(comPortName, comBaudRate):
  global comPort

  print("Loopback Test on " + comPortName+" at " + str(comBaudRate) + " baud")
  time.sleep(1)

  comPort = serial.Serial \
            (
              port     = comPortName,
              baudrate = comBaudRate,
              parity   = serial.PARITY_NONE,
              stopbits = serial.STOPBITS_ONE,
              bytesize = serial.EIGHTBITS
            )

  threading.Thread(target=TransmitThread).start()
  threading.Thread(target=ReceiveThread).start()

  try:
    while True:
      time.sleep(1)
  except KeyboardInterrupt:
    print("")
  finally:
    comPort = None

if __name__ == "__main__":
  if len(sys.argv) <= 1:
    if windows            : LoopbackTest("COM1",         9600)
    else                  : LoopbackTest("/dev/serial0", 9600)
  elif len(sys.argv) <= 2 : LoopbackTest(sys.argv[1],    9600)
  else                    : LoopbackTest(sys.argv[1],    int(sys.argv[2]))