distance.ino

void setup() {
  pinMode (2,OUTPUT);//attach pin 2 to vcc
  pinMode (5,OUTPUT);//attach pin 5 to GND
  // initialize serial communication:
  Serial.begin(9600);
}

void loop()
{
digitalWrite(2, HIGH);
  // establish variables for duration of the ping,
  // and the distance result in inches and centimeters:
  long duration, inches, cm;

  // The PING))) is triggered by a HIGH pulse of 2 or more microseconds.
  // Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
  pinMode(3, OUTPUT);// attach pin 3 to Trig
  digitalWrite(3, LOW);
  delayMicroseconds(2);
  digitalWrite(3, HIGH);
  delayMicroseconds(5);
  digitalWrite(3, LOW);

  // The same pin is used to read the signal from the PING))): a HIGH
  // pulse whose duration is the time (in microseconds) from the sending
  // of the ping to the reception of its echo off of an object.
  pinMode (4, INPUT);//attach pin 4 to Echo
  duration = pulseIn(4, HIGH);

  // convert the time into a distance
  inches = microsecondsToInches(duration);

  Serial.print(inches);
  Serial.println();

  delay(100);
}

long microsecondsToInches(long microseconds)
{
  // According to Parallax's datasheet for the PING))), there are
  // 73.746 microseconds per inch (i.e. sound travels at 1130 feet per
  // second).  This gives the distance travelled by the ping, outbound
  // and return, so we divide by 2 to get the distance of the obstacle.
  // See: http://www.parallax.com/dl/docs/prod/acc/28015-PING-v1.3.pdf
  return microseconds / 74 / 2;
}

distance_server.py

#!/usr/bin/python
import serial
import syslog
import time
import collections

# change to your Arduino serial device
port = '/dev/tty.usbmodemfa141'

distance = 0

def arduino_thread():
    ard = serial.Serial(port,9600,timeout=5)
    global distance

    while True:
        # Serial read section
        msg = ard.readline().strip()
        if msg:
            distance = int(msg)

import threading
t = threading.Thread(target=arduino_thread, args=())
t.daemon = True
t.start()

# flask app
from flask import Flask, jsonify
from flask_cors import cross_origin
app = Flask(__name__)

@app.route('/')
@cross_origin()
def hello_world():
    return jsonify({'distance': distance})

if __name__ == '__main__':
    app.run()

requirements.txt

Flask
Flask-Cors