Python serial.read() doesn't read data from Arduino in the first loop

Question

I am a hardware design engineer trying to play with high-level-languages recently. These are my first Python codes. I am very far from OOP and all high-level-language shenanigans. I loved Python very much but I am at the very beginning of learning it. Thanks for your help in advance.

I am trying to read serial data from Arduino. This code is running on Raspberry Pi 3+. It doesn't read in the first loop.

Here is the Arduino code that sends dummy data upon request:

String data = "";
void setup(){
 
  Serial.begin(115200);
}
 
void loop(){
 
  while (Serial.available() > 0) {
    data = Serial.readStringUntil('\n');
     if(data=="$ACONSP?"){
      Serial.println("$ACONSP,3600,100,100,200,300,400,500,600,700");
      }
      else if (data == "$ASTAT"){
      Serial.println("$ASTAT,0,1,0,0,1,0,1,0");
      }
      else if (data == "$AENV"){
      Serial.println("$AENV,234.2,49.3,27.7,41.6,24.9,39.9,0,0");
      }
  }
}

Here is the Python code that sends request and read the response from Arduino and write it into SQLite.

from time import sleep
import serial

PowerResponseKeys = ['head','timePassed','Ch0Consp','Ch1Consp','Ch2Consp','Ch3Consp','Ch4Consp','Ch5Consp','Ch6Consp','Ch7Consp']
StatusResponseKeys = ['head','Ch0Stat','Ch1Stat','Ch2Stat','Ch3Stat','Ch4Stat','Ch5Stat','Ch6Stat','Ch7Stat']
EnvironmentResponseKeys = ['head','Voltage','Frequency','InTemp','InHumidity','ExtTemp','ExtHumidity','DoorSwitch','DoorRelay']
channel = ["A","B","C"]
request_type = ["CONSP?", "STAT", "ENV"]
ser = serial.Serial("/dev/cu.usbserial-1420", baudrate=115200, timeout=0)
counter = 0

#The function that sends the "requestline= "$"+channel+request_type" string to Arduino and read the response
def request(channel,request_type):
    line = ''
    responseKey = []
    requestline= "$"+channel+request_type
    if request_type == 'CONSP?':
        responseKey = PowerResponseKeys
    elif request_type == 'STAT':
        responseKey = StatusResponseKeys
    elif request_type == 'ENV':
        responseKey = EnvironmentResponseKeys
    else:
        pass
    ser.write(requestline.encode())
    sleep(2)
    if ser.inWaiting() > 0:
        line = str(ser.readline().decode('ascii').strip()).split(",")
    response_dict = dict(zip(responseKey, line))
    return response_dict

If I write this: if len(request(channel[0], request_type[0])) > 0: if statement, it waits for sometime and return the right response. But it waits for a long time.

while 1:
    if counter < 2:
        if len(request(channel[0], request_type[0])) > 0:
            Write2DB(request(channel[0], request_type[0]))
        else:
            pass
        counter += 1
    else:
       break:
       

If I do if counter < 1: instead of if counter < 2:, it doesn't return anything. So I think it is all about "not getting the response string on time"

This loop needed to loop many times:

while True:
    if counter <3:
        request(channel[0],request_type[0])
    else:
        break

If I change the sleep(2) to sleep(1) or a lesser value, it never reads the response from Arduino.

What I need is, reading the response from Arduino faster, in the first loop if it is possible without waiting more than 2-3 seconds. I've read the serial library documentation, but couldn't figure out what solves my problem.

I assume some kind of handshake between Python and Arduino will solve the problem but am not sure.

What do you recommend? What should I do?

Thanks again.

Answer 1

Changed timeout=0 to timeout=1 and it solved the problem.

ser = serial.Serial("/dev/cu.usbserial-1420", baudrate=115200, timeout=0)