Cherrypy and JSON Arduino web interface

First of all, I did'nt think about telling you about that in your previous question, but a while back I wrote a software called pyaler that does exactly what you want (except it did not support long polling requests, as it is (was?) a wsgi limitation).

To answer your question, why don't you make your form a javascript query that sends the action, and gets the result as JSON that you can parse and update your current page with the result? That's way more elegant, simple and 2013...

Sadly I can't really tell, given your code, why you're not getting the result. It's too much over-sophisticated to understand if it really does what you want it to do... KISS!

Avoid doing anything at the module scope, except if you put it in if __name__ == "__main__", or the day you'll want to extend your module by importing it, you'll execute incidentally some code, and it forces making a better design for your code.

You can take the InterruptableThread() class out of your timeout function, and give it the default as a parameter. InterruptableThread(default) and def __init__(self, default): self.result = default. But talking about that part, why do you do such over-sophisticated thing whereas you got a timeout argument you can use in when you create your serial connection?

Here is a slight modification I'd make to your code:

# -*- coding: utf-8 -*-

import cherrypy, functools, json, uuid, serial, threading, webbrowser, time

def arduino_connect(timeout=0):
    try:
        ser=serial.Serial('COM4', 9600, timeout=timeout)
        time.sleep(2)
        ser.write('1')
        return ser
    except:
        raise Exception('Arduino not detected. Moving on')

class ArduinoActions(object):
    def __init__(self, ser):
        self.ser = ser

    def get_data(self):
        content = ""
        while True:
            print('reading...')
            data = self.ser.read().encode('utf-8')
            if not data or data == '*':
                return content
            content += data

    def turn_led_on(self):
        ser.write('2')
        time.sleep(2)
        print('wrote led on to port')

    def turn_led_off(self):
        ser.write('2') # Replace with the value to tur the led off
        time.sleep(2) 
        print('wrote to led off port')

class DemoServer(ArduinoActions):
    def __init__(self, ser):
        ArduinoActions.__init__(self, ser)
        with open('index.html', 'r') as f:
            self.index_template = f.read()

    @cherrypy.expose
    def index(self):
        return self.index_template

    @cherrypy.expose
    def action(self, command):
        state = 'ready'
        if command == "on":
            content = self.turn_led_on()
        elif command == "off":
            content = self.turn_led_off()
        else:
            content = 'unknown action'
            state = 'failure'
        return {'state': state, 'content': content}

    @cherrypy.expose
    def read(self):
        content = self.get_data()
        time.sleep(1)
        # set content-type to 'application/javascript'
        return content

if __name__ == '__main__':
    ser = arduino_connect(5)
    # t = threading.Timer(0.5, webbrowser.open, args=('http://localhost:8080',))
    # t.daemon = True
    # t.start()
    cherrypy.quickstart(DemoServer(), config='config.conf')

In your javascript code, you you're calling the yell resource that returns literally nothing. You'd better make an action method (as I modified the given python code) and a separate read() method. So you the action method will act on the arduino by writing bytes, thus commands to the arduino, and the read method will read the output.

As the webserver may create parallel calls to the read/write method on the serial object, and you can't read in parallel the same object, you may want to make an independant thread, by creating a new class that inherits from threading.Thread, you implement an infinite loop reading the output of the serial (by giving the serial object as parameter to that class' __init__ function). Then you push each new content data to a list, if you want to keep a log of all previous data, or a Queue.Queue if you want only the last reading returned. Then from ArduinoActions, in the read() method you just need to return that list that will grow with any new reading from the arduino, and thus make a log of all the data (or get the last data if you have a queue).

$(function() {
    function update(command) {
        // if you give a command argument to the function, it will send a command
        if (command) {
            $.getJSON('/action?command='+command);
        }
        // then it reads the output
        $.getJSON('/read, {}, function(data) {
        if (data.state !== 'failure' && data.content !== '') {
            $('.notice').text(data.content);
            $('.notice').hide().fadeIn('fast');
            setTimeout(function () { $('.notice').fadeOut('fast'); }, 1500);
        }
        // and rearms the current function so it refreshes the value
        setTimeout(update(), 2); // you can make the updates less often, you don't need to flood your webserver and anyway the arduino reading are blocking
    });
}
update();
});

Always use === or !== in javascript so type don't get coerced. You can call again the function less often If you do not valuate a javascript argument, it is set to undefined per default.

That's only a little update on what you wrote, it's getting late now, so I hope you'll make something nice out of that!

HTH