Arduino code not running when getting pre-determined string from python on serial

Question

I am trying to have my arduino uno run when code is sent to it, however, nothing happens except the lights blinking back and forth for a second when it is sent and then nothing. I am just sending a string on serial, and using an if statement so it should be super straight forward but I am not sure what is happening to cause it not to work. Code below, any help would be awesome. Python

import serial, time
arduino = serial.Serial('/dev/ttyUSB0', 9600, timeout=1)
cmd = ''
while cmd != '0':
        cmd = input('Enter a cmd ')
        arduino.write(cmd.encode('ascii'))

Arduino

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

void loop() {
    delay(100);
    if (Serial.available() > 0) {
    String stringFromSerial = Serial.readString();
    if (stringFromSerial == "1") {
        Serial.println("1");

    } else if (stringFromSerial == "2") {
        Serial.println("2");

    } else if (stringFromSerial == "3") {
        Serial.println("3");

    } else {
        Serial.println("Not recognized cmd");

    }
  }
}

Update: Thanks for the help, I have updated the code to what actually works.

Answer 1

As indicated by hcheung, the string you want to send isn't correct.

Looking at the w3schools and programiz, I suggest you do something similar to

cmd = 'fwd'
arduino.write(cmd.encode('ascii'))

Or, for non-ASCII character commands, you can encode as 'UTF-8'. But I doubt you'd be happy with those encodings.

arduino.write(cmd.encode(encoding='UTF-8'))

You could also send multiple commands from Python like so:

in = ''
while in != '0':
    in = input('Enter a command: ')
    arduino.write(in.encode('ascii'))
    # this loop will exit if you enter '0',
    # but will first send the exit command to the Arduino

and receive multiple commands on the Arduino side:

void loop() {
    delay(100);
    if (Serial.available() > 0) {
    String stringFromSerial = Serial.readString();
    if (stringFromSerial == "1") {
        // do something for command 1

    } else if (stringFromSerial == "2") {
        // do something for command 2

    } else if (stringFromSerial == "3") {
        // do something for command 3

    } else {
        // do an exit command perhaps

    }
}