javascript - Update and render a value from Flask periodically

Question

I want to display my CPU usage dynamically. I don't want to reload the page to see a new value. I know how to get the CPU usage in Python. Right now I render a template with the value. How can I continually update a page with a value from Flask?

@app.route('/show_cpu')
def show_cpu():
    cpu = getCpuLoad()
    return render_template('show_cpu.html', cpu=cpu)

not reloading the page means you have to execute code from the client, which means you have to use javascript. Also, when you say CPU usage do you mean your server's? — Nadir Sampaoli
Yup, you have to use JavaScript to make a query to the server to get an update on the CPU usage. Not possible to do this entirely from the server side. — aychedee
If you established a websocket connection, then the server could push updates to the client. But you would still be using JS to create the connection and deal with the updates from the server. — aychedee

Depado Depado · Accepted Answer · 2014-08-29T08:05:14

Using an Ajax request

Python

@app.route('/_stuff', methods= ['GET'])
def stuff():
    cpu=round(getCpuLoad())
    ram=round(getVmem())
    disk=round(getDisk())
    return jsonify(cpu=cpu, ram=ram, disk=disk)

Javascript

function update_values() {
            $SCRIPT_ROOT = {{ request.script_root|tojson|safe }};
            $.getJSON($SCRIPT_ROOT+"/_stuff",
                function(data) {
                    $("#cpuload").text(data.cpu+" %")
                    $("#ram").text(data.ram+" %")
                    $("#disk").text(data.disk+" %")
                });
        }

Using Websockets

project/app/views/request/websockets.py

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

# OS Imports
import json

# Local Imports
from app import sockets
from app.functions import get_cpu_load, get_disk_usage, get_vmem

@sockets.route('/_socket_system')
def socket_system(ws):
    """
    Returns the system informations, JSON Format
    CPU, RAM, and Disk Usage
    """
    while True:
        message = ws.receive()
        if message == "update":
            cpu = round(get_cpu_load())
            ram = round(get_vmem())
            disk = round(get_disk_usage())
            ws.send(json.dumps(dict(received=message, cpu=cpu, ram=ram, disk=disk)))
        else:
            ws.send(json.dumps(dict(received=message)))

project/app/__init__.py

# -*- coding: utf-8 -*-
from flask import Flask
from flask_sockets import Sockets


app = Flask(__name__)
sockets = Sockets(app)
app.config.from_object('config')
from app import views

Using Flask-Websockets made my life a lot easier. Here is the launcher : launchwithsockets.sh

#!/bin/sh

gunicorn -k flask_sockets.worker app:app

Finally, here is the client code :
custom.js
The code is a bit too long, so here it is.
Note that I'm NOT using things like socket.io, that's why the code is long. This code also tries to reconnect to the server periodically, and can stop trying to reconnect on a user action. I use the Messenger lib to notify the user that something went wrong. Of course it's a bit more complicated than using socket.io but I really enjoyed coding the client side.

javascript - Update and render a value from Flask periodically

1 Answers

Using an Ajax request

Using Websockets