Data in serial comm going more than expected

[sud_shenoy]

I have been trying to get serial communication to work with using USB to Raspberyy Pi with Arduino Nano. I have got down most of the things correct; I want the Nano to respond only when I send a request from Pi. The problem I am facing now is that the Nano is sending to Rpi one more time than I am expecting. I can of course ignore this, but I want to know if its a problem with my understanding of how the serial comm works.

Attaching the snippets of the relevant code,

Arduino code;

void loop() {
  readSerialPort();
  if (msg == "data") 
  {
      Serial.print(Int1);
      Serial.print("x");
      Serial.print(Int2);
      Serial.print("x");
      Serial.print(Int3);
  }
  delay(1);  
}

void readSerialPort() {
  msg = "";
  if (Serial.available()) {
    delay(10);
    while (Serial.available() > 0) {
      msg += (char)Serial.read();
    }
    Serial.flush();
  }
}

Python code at the Raspberry Pi end;

while True:
            cmd="data"
            arduino.write(cmd.encode())
            if  arduino.inWaiting()>0: 
                answer=str(arduino.readline(),'utf-8')
                print("---> {}".format(answer))

This is how I am getting the integers in python,

[Whandall]

There is a serial input bascis tutorial, which you should study.

Serial Input Basics - updated

Updated Version Please note that this is a revised version of the advice in this earlier Thread which has become very long. As far as possible I have kept the code examples identical or simplifed them slightly. It should not be necessary to refer to the older Thread, but feel free to do so. Contents The following sections are in this Tutorial Introduction Serial data is slow by Arduino standards Example 1 - Receiving single characters Why code is organized into functions Exampl…

On a Nano don't use Strings and on any single thread system don't use delay.

[Mod edit]
See new topic for discussion on the merits of char arrays Vs Strings

[PerryBebbington]

The discussion past this point was not really an answer to the OP's question, but was worth continuing so I have moved it to a new topic.