circuits + React

I’ve been hearing lots of good things about React (a JavaScript library to build User Interfaces) and recently came across the several tutorials that have a backend implementation in:

I felt that there was one missing in particular and that of course is:

For those not familiar with circuits it is:

  • A Python Application Framework
  • Supports a loosely coupled architecture
  • Is fully event-driven (i.e: react!)
  • Supports Asynchronous I/O
  • Supports Coroutines
  • and more more...

Here is the same implementation of the above backends using circuits:

from os import environ
from json import dumps, loads

from circuits.web import Server, Controller, Static

class Comments(Controller):

    channel = "/comments.json"

    def index(self, **data):
        with open("comments.json", "r") as f:
            comments = loads(

        if self.request.method == "POST":
            comments.append({"author": data["author"], "text": data["text"]})

            with open("comments.json", "w") as f:

        self.response.headers["Content-Type"] = "application/json"
        self.response.headers["Cache-Control"] = "no-cache"

        return dumps(comments)

(Server(("", int(environ.get("PORT", 3000)))) + Comments() + Static(docroot="public")).run()

Now whilst this may seem very similar to the Python+Flask example using circuits has several advantages:

  • We can easily add new functionality by “composing” and “registering” more Component(s)

Let’s say we want to password protect our resource without modifying the existing code?


Write a Auth Component:

from hashlib import md5

from circuits import handler, Component
from import check_auth, basic_auth

class Auth(Component):

    channel = "web"

    realm = "Comments"
    users = {"admin": md5("admin").hexdigest()}

    @handler("request", priority=1.0)
    def on_request(self, event, request, response):
        if request.path != "/comments.json":

        if not check_auth(request, response, self.realm, self.users):
            return basic_auth(request, response, self.realm, self.users)

And add this newly created component into the mix:

(Server(("", int(environ.get("PORT", 3000)))) + Auth() + Comments() + Static(docroot="public")).run()

Enjoy! And happy hacking! :)