float flow = 500.06;
void setup() {
  Serial.begin( 9600 );}
void loop() {
    if (Serial.available()>0) {
        if (Serial.read() == 'R') {
             Serial.print(flow)
             Serial.write("\n");
        }
    }
}

#! /usr/bin/env python
import serial
from time import sleep
ser = serial.Serial(port='/dev/serial0',parity=serial.PARITY_NONE,
        stopbits=serial.STOPBITS_ONE,bytesize=serial.EIGHTBITS,timeout=1)
# Wait to read from Arduino
while 1:
        try:
                time.sleep(10)
                ser.write("R")
                myData = ser.readline()
                print myData
        except KeyboardInterrupt:
                exit()