serial.serialutil.SerialException: [Errno 16] coul

I'm trying to print serial output from Arduino Uno onto my screen using Pyserial python library.

Here is my Arduino code. It just produces and prints random numbers to serial monitor:

void setup() {
Serial.begin(9600);

}

void loop() {
    long rand = random(10);
    Serial.print(rand);
}

My python code is just supposed to print the values from serial onto the command line, here is the code:

#!/usr/bin/python

import serial

ser = serial.Serial("/dev/ttyACM0",9600)
while True:
    thing = ser.readline()
    print(thing)

While Arduino is printing random numbers to the serial monitor, I run my python script and get the error:

Traceback (most recent call last):
  File "/home/archimedes/anaconda3/lib/python3.6/site-packages/serial/serialposix.py", line 265, in open
    self.fd = os.open(self.portstr, os.O_RDWR | os.O_NOCTTY | os.O_NONBLOCK)
OSError: [Errno 16] Device or resource busy: '/dev/ttyACM0'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "pythonSerialTest.py", line 6, in <module>
    ser = serial.Serial("/dev/ttyACM0",9600)
  File "/home/archimedes/anaconda3/lib/python3.6/site-packages/serial/serialutil.py", line 240, in __init__
    self.open()
  File "/home/archimedes/anaconda3/lib/python3.6/site-packages/serial/serialposix.py", line 268, in open
    raise SerialException(msg.errno, "could not open port {}: {}".format(self._port, msg))
serial.serialutil.SerialException: [Errno 16] could not open port /dev/ttyACM0: [Errno 16] Device or resource busy: '/dev/ttyACM0'

回答1:

You can't have two programs use the same serial port.

Close the serial monitor in the Arduino IDE.

PS: You are also trying to read lines in Python, but you aren't sending them from the Arduino.

Print the numbers as lines with Serial.println(rand);.

回答2:

I was getting the resource busy error because Python was trying to access the serial monitor, but since I uploaded my code to Arduino with the command: sudo make upload monitor clean, my PC was getting access to the serial monitor from Arduino, which prevented Python from being able to access the serial monitor from Arduino. Now I just upload the code to Arduino with sudo make upload clean and exclude the command monitor if I plan to use Python to access the serial monitor.