PySerial weird bytes at the beginning

Question

I'm trying out Python 3.9 to Arduino DUE serial communication for the first time using PySerial, but I'm encountering an interesting issue. Every time I send some data, the Arduino returns it but prefixed with some unknown characters(see image bellow). The baud rates are matched.

The Issue

Here is the Python code

ser = serial.Serial('/dev/cu.usbmodem11301', 115200)
ser.write(b'hello')
ser.close()

And here is the arduino code:

if (Serial.available() > 0) {
  String command = Serial.readString();
  Serial.println(command);
}

I've tried doing everything: running ser.flush() before sending the data, sleep() after sending the data, ser.write(bytes("hello", "utf-8")) etc.. but the issue still persisted.

Does anyone know what could be the cause of this?

Answer 1

While this doesn't exactly solve the source of the problem (transmitting unwanted null characters), one solution is to add the substring line as shown below.

if (Serial.available() > 0) {
  String command = Serial.readString();
  command = command.substring(command.lastIndexOf('\0'));
  Serial.println(command);
}