PySerial. Unable to make any input during serial reading

Question

So, I am trying to use serial communication with Arduino using python by using pyserial library. I have a while True loop where I am reading data sent from the Arduino, however, I want to be able to send something as well from Arduino by using ser.write, However, I am unable to do so.

import serial
import sys
import time
import pynput


from pynput import keyboard


ser = serial.Serial('COM4', baudrate = 9600, timeout = 20)





while True:

        print(ser.readline().decode('utf-8'))






def on_press(key):
    try:
        print('alphanumeric key {0} pressed'.format(
            key.char))
    except AttributeError:
        print('special key {0} pressed'.format(
            key))

def on_release(key):
    print('{0} released'.format(
        key))
    if key == keyboard.Key.esc:
        return False


with keyboard.Listener(
        on_press=on_press,
        on_release=on_release) as listener:
    listener.join()

listener = keyboard.Listener(
    on_press=on_press,
    on_release=on_release)
listener.start()

I am also using pynput library to look for keys pressed on the keyboard which I will modify later for example if key 0 is pressed ser.write something and etc. I just can't get it to work so it will print whatever key I am pressing its always waiting for ser.readline. Could anybody help me fix this?

In conclusion, I want to be able to input some key during serial reading.

Thanks

Hello and welcome to StackOverflow! Would you mind editing your post and showing us what output/errors you're getting? — Daniel Walker

Vincent Vincent · Accepted Answer · 2020-05-22T17:47:32

Your problem is basically that the code below the while True loop is never executed, since the loop never ends. So you basically have to use something called threading where you split your process into parts and run the parts in seperate threads. Below you can see an example of threading which you can use as is. The KeyboardThread handles all keyboard input and the SerialReaderThread handles the serial read calls.

from pynput import keyboard
import threading
import time
import serial
import sys

class SerialReaderThread(threading.Thread):
    def run(self):
        ser = serial.Serial('COM4', baudrate = 9600, timeout = 20)
        while True:
            print(ser.readline().decode('utf-8'))

class KeyboardThread(threading.Thread):
    def run(self):
        def on_press(key):
            try:
                print('alphanumeric key {0} pressed'.format(key.char))

                # quit when q is pressed
                if key.char == "q":
                    exit()
            except AttributeError:
                print('special key {0} pressed'.format(key))

        def on_release(key):
            print('{0} released'.format(
                key))
            if key == keyboard.Key.esc:
                return False


        with keyboard.Listener(on_press=on_press, on_release=on_release) as listener:
            listener.join()

        listener = keyboard.Listener(on_press=on_press, on_release=on_release)
        listener.start()

serial_thread = SerialReaderThread()
keyboard_thread = KeyboardThread()

serial_thread.start()
keyboard_thread.start()
serial_thread.join()
keyboard_thread.join()

You can learn more about threading and how to use it here: https://www.tutorialspoint.com/python3/python_multithreading.htm

PySerial. Unable to make any input during serial reading

2 Answers