[Tkinter] Thread for serial Reading shows an error

[eabs86]

I created a python interface to display some information on the screen while collecting data through the serial port. The communication is made with an ATmega micro-controller. The serial port should send data once I hit the Start button, then it sends a command character to the micro-controller ('g' = go). If I hit the Close button the data should stop being sent (Close button sends another command character, 's' = stop).

I know that it was not possible to create another loop inside the program when using tkinter (can cause crashes and malfunctioning). The solution would be create threads. So I created a Thread to read the data in parallel of tkinter loop. Each block of data sent ends with a '\n', so I had to use the readline() command.

Here is the simplified code

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from tkinter import * from tkinter import ttk import time import serial import threading   ser = serial.Serial(         port = 'COM3',         baudrate=9600,         parity=serial.PARITY_NONE,         stopbits=serial.STOPBITS_ONE,         timeout=None,         bytesize= serial.EIGHTBITS)   ser.flushInput() if ser.isOpen() == False:     ser.open()   def raise_frame(frame):     frame.tkraise()   def finish():       ser.write('s'.encode())     time.sleep(1)     ser.close()     root.destroy()   def start():     ser.write('g'.encode())     thread.start()   def readSerial():     while True:         DATA = ser.readline()         print(DATA)   def force_close(event):     ser.write('s'.encode())     time.sleep(1)     ser.close()     root.destroy()     root = Tk() root.attributes("-fullscreen", True) w, h = root.winfo_screenwidth(), root.winfo_screenheight()   f1 = Frame(root) f1.place(x=0,y=0, relheight=1, relwidth=1)   # ============================================================================= # Start Button # ============================================================================= btn_start=Button(f1, text="Start",font = ("Arial Bold",30), command = start) btn_start.pack(padx=10,pady=30, side = BOTTOM)   # ============================================================================= # Close Button # ============================================================================= close_value=BooleanVar() btn_close=Button(f1, text="Close",font = ("Arial Bold",30), command=finish) btn_close.pack(padx=10,pady=30, side = BOTTOM)   thread=threading.Thread(target=readSerial) thread.daemon=True root.bind('<Escape>',force_close) raise_frame(f1) root.mainloop()

The problem is: everytime that I close the application this error appears:

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Exception in thread Thread-8: Traceback (most recent call last):   File "C:\Users\apoco\Anaconda3\lib\threading.py", line 916, in _bootstrap_inner     self.run()   File "C:\Users\apoco\Anaconda3\lib\threading.py", line 864, in run     self._target(*self._args, **self._kwargs)   File "<ipython-input-2-838b466f09c9>", line 41, in readSerial     DATA = ser.readline()   File "C:\Users\apoco\Anaconda3\lib\site-packages\serial\serialwin32.py", line 269, in read     win32.ResetEvent(self._overlapped_read.hEvent) AttributeError: 'NoneType' object has no attribute 'hEvent'

Does anyone knows how to handle with this error?

Best Regards,

Emmanuel