Running Python under node.js

grantc66

Hi,

A few weeks ago I started looking into getting notifications onto the mirror from python. Whilst it was relatively straight forward to run python within a shell from the node-helper, I ran into various problems with user privileges and environments.

To get around this I had a play with rabbitmq. Using amqp for the node end and pika for the python. This opens up a whole world of possibilities for my mirror without having to learn javascript (above the basics & plagiarising code snippets from the built in modules) .

node-helper end looks like. Sorry it’s a bit messy & I went overboard on the error capture.

var amqp = require("amqplib/callback_api");

PStart: function starter() {
const self = this;
  amqp.connect("amqp://localhost", function(err, conn) {
    if (err) {
      console.error("[AMQP]", err.message);
      return setTimeout(starter, 1000);
    }
    conn.on("error", function(err) {
      if (err.message !== "Connection closing") {
        console.error("[AMQP] conn error", err.message);
      }
    });
    conn.on("close", function() {
      console.error("[AMQP] reconnecting");
      return setTimeout(starter, 1000);
    });
    console.log("[AMQP] connected");
    amqpConn = conn;

  amqpConn.createChannel(function(err, ch) {
    if (closeOnErr(err)) return;
    ch.on("error", function(err) {
      console.error("[AMQP] channel error", err.message);
    });
    ch.on("close", function() {
      console.log("[AMQP] channel closed");
    });

    ch.prefetch(10);
    ch.assertQueue("message", { durable: false }, function(err, _ok) {
      if (closeOnErr(err)) return;
      ch.consume("message", function(msg) {
try {
 var fp = JSON.parse(msg.content.toString());
    ch.ack(msg);
    } catch (e) {
      closeOnErr(e);
    }
                if (fp[0].data == "data"){
                self.sendData({"PlrStat": fp[0].PlrStat, "TrkNxt":fp[0].TrkNext, "Station": fp[0].Station, "Said": fp[0].Said);
                } else if (fp[0] == "status") {
                console.log("[MMM-Radio]" + fp[0].status);
                } else {
                console.log("Got something");
                console.log(msg);
                console.log(fp[0].data);}
})}, { noAck: false });
      console.log("Worked");
      });
});
}  });

function closeOnErr(err) {
  if (!err) return false;
  console.error("[AMQP] error", err);
  amqpConn.close();
  this.Pstart();
  return true;
}

Python end:

import pika

def to_node(message):
    try:
        channel.basic_publish(exchange='',
                              routing_key='message',
                              body=json.dumps(message))
    except Exception:
        connection = pika.BlockingConnection(pika.ConnectionParameters(host='localhost'))
        channel = connection.channel()
        channel.queue_declare(queue='message')
        channel.basic_publish(exchange='',
                              routing_key='message',
                              body=json.dumps(message))

The bit in the exception is the initial setup for the connection, it does occasionally time out so re-establish if the publishing doesn’t work.

Some useful tutorials on rabbitmq can be found here

Hope this is a help to some of you who know very little about js & do all the complicated stuff with other languages.

sdetweil

@grantc66 cool, thanks…

for node, you could have spun off a long running python app,
and added data.on() event handlers in javascript node_helper to get called each time the python app wrote to the console (stdout)… which could have been json data, or whatever text you liked

const {spawn} = require('child_process')

const child = spawn('pwd');

child.stdout.on('data', (data) => {
  console.log(`child stdout:\n${data}`);
});

child.stderr.on('data', (data) => {
  console.error(`child stderr:\n${data}`);
});

timpaines

Node js is one of the powerful tools of programming and using this if you are working on python it help you a lot. printer offline fix helped me to know more about python.