How can I communicate between running python code and nodejs
I would like to run python code and communicate with an expressjs express node. So far, I can get my nodejs server to call python functions through one of two mechanisms to invoke a python task or talk to the zerorpc python server.
First, a la http://www.sohamkamani.com/blog/2015/08/21/python-nodejs-comm/ , this works:
var express = require( "express" );
var http = require( "http" );
var app = express();
var server = http.createServer( app ).listen( 3000 );
var io = require( "socket.io" )( server );
app.use( express.static( "./public" ) );
io.on( "connection", function( socket ) {
// Repeat interval is in milliseconds
setInterval( function() {
var spawn = require( 'child_process' ).spawn,
py = spawn( 'python', [ 'mytime.py' ] ),
message = '';
py.stdout.on( 'data', function( data ) {
message += data.toString();
});
py.stdout.on( 'end', function() {
socket.emit( "message", message );
});
}, 50 );
});
Where is mytime.py
from datetime import datetime
import sys
def main():
now = datetime.now()
sys.stdout.write( now.strftime( "%-d %b %Y %H:%M:%S.%f" ) )
And from zerorpc http://www.zerorpc.io/ if this python code is running:
from datetime import datetime
import sys
import zerorpc
class MyTime( object ):
def gettime( self ):
now = datetime.now()
return now.strftime( "%-d %b %Y %H:%M:%S.%f" )
s = zerorpc.Server( MyTime() )
s.bind( "tcp://0.0.0.0:4242" )
s.run()
This nodejs code works:
var express = require( "express" );
var http = require( "http" );
var app = express();
var server = http.createServer( app ).listen( 3000 );
var io = require( "socket.io" )( server );
var zerorpc = require( "zerorpc" );
var client = new zerorpc.Client();
client.connect( "tcp://127.0.0.1:4242" );
app.use( express.static( "./public" ) );
io.on( "connection", function( socket ) {
// Repeat interval is in milliseconds
setInterval( function() {
client.invoke( "gettime", function( error, res, more ) {
socket.emit( "message", res.toString( 'utf8' ) );
} );
}, 50 );
});
But what I would like to do, instead of just calling the python functions, I would like to start a separate python process and send messages to a nodejs server, which listens for them and then processes them. I experimented with the standard socket pattern, but if I try to set up a python server with zerorpc on the same port as the nodejs express server, it gives zmq.error.ZMQError: Address an already used error.
I know I am not thinking about this right - I know that I am missing some logic of inter-process communication due to my naivety here - so if there is a better way to make sending messages from a python process using nodejs while listening to the server, I am all ears ...
Any ideas?
Thanks in advance!
For those trying to figure it out, here is the solution thanks to Zeke Alexandre Nierenberg
For node.js server code:
var express = require( "express" );
var app = express();
var http = require( "http" );
app.use( express.static( "./public" ) ); // where the web page code goes
var http_server = http.createServer( app ).listen( 3000 );
var http_io = require( "socket.io" )( http_server );
http_io.on( "connection", function( httpsocket ) {
httpsocket.on( 'python-message', function( fromPython ) {
httpsocket.broadcast.emit( 'message', fromPython );
});
});
and the python code that sends messages to it:
from datetime import datetime
from socketIO_client import SocketIO, LoggingNamespace
import sys
while True:
with SocketIO( 'localhost', 3000, LoggingNamespace ) as socketIO:
now = datetime.now()
socketIO.emit( 'python-message', now.strftime( "%-d %b %Y %H:%M:%S.%f" ) )
socketIO.wait( seconds=1 )
Voila!
I'm having problems with socketIO version ...
so, this is my solution:
NodeJS:
var app = require("express")();
var http = require('http').Server(app);
var bodyParser = require('body-parser');
app.use(bodyParser.json())
app.post('/',function(req,res){
var msg=req.body.msg;
console.log("python: " + msg);
});
http.listen(3000, function(){
console.log('listening...');
});
in Python:
import requests
import json
url = "http://localhost:3000"
data = {'msg': 'Hi!!!'}
headers = {'Content-type': 'application/json', 'Accept': 'text/plain'}
r = requests.post(url, data=json.dumps(data), headers=headers)