application.py

from flask_socketio import SocketIO, emit
from flask import Flask, render_template, url_for, copy_current_request_context
from random import random
from time import sleep
from threading import Thread, Event
import serial
import struct
import time
from datetime import datetime

app = Flask(__name__)
app.config['SECRET_KEY'] = 'secret!'
app.config['DEBUG'] = True


#serial data
arduino = serial.Serial(port='/dev/ttyS0',
                    baudrate = 9600,
                    parity=serial.PARITY_NONE,
                    stopbits=serial.STOPBITS_ONE,
                    bytesize=serial.EIGHTBITS,
                    timeout=1)

#turn the flask app into a socketio app
socketio = SocketIO(app, async_mode=None, logger=True, engineio_logger=True)

#random number Generator Thread
thread = Thread()
thread_stop_event = Event()

def NumberGenerator():
    """
    Generate a random number every 1 second and emit to a socketio instance (broadcast)
    Ideally to be run in a separate thread?
    """
    #infinite loop of magical random numbers
    print("Starting to receive data")
    while not thread_stop_event.isSet():


        lista = []
        while True:

            data = arduino.read()
            if data:
                if data == b'f':
                    data2 = arduino.read(4)

                    lista.append(struct.unpack('f',data2)[0])
                    pass
                if data == b';':
                    break
                else:
                    pass

        print(lista)
        now = datetime.now()
        timestamp = now.strftime("%H:%M:%S")
        socketio.emit('newnumber', {'sin': lista[0], 'cos': lista[1], 'tan':lista[2], 'timestamp': timestamp}, namespace='/test')

        socketio.sleep(0.1)


@app.route('/')
def index():
    #only by sending this page first will the client be connected to the socketio instance
    return render_template('index.html')

@socketio.on('connect', namespace='/test')
def test_connect():
    # need visibility of the global thread object
    global thread
    print('Client connected')

    #Start the random number generator thread only if the thread has not been started before.
    if not thread.isAlive():
        print("Starting Thread")
        thread = socketio.start_background_task(NumberGenerator)

@socketio.on('disconnect', namespace='/test')
def test_disconnect():
    print('Client disconnected')


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