index.js

const express = require('express')
const {spawn} = require('child_process');
const app = express()
const port = 3000
app.get('/', (req, res) => {
 
// var dataToSend;
 // spawn new child process to call the python script
 // const python = spawn('python', ['script1.py']);
// const python = spawn('python', ['script.py','node.js','python']);
 // collect data from script
// python.stdout.on('data', function (data) {
//  console.log('Pipe data from python script ...');
//  dataToSend = data.toString();
// });
 // in close event we are sure that stream from child process is closed
// python.on('close', (code) => {
// console.log(`child process close all stdio with code ${code}`);
 // send data to browser
// res.send(dataToSend)
// });
 
//})
//app.listen(port, () => console.log(`Example app listening on port 
//${port}!`))

var largeDataSet = [];
 // spawn new child process to call the python script
 const python = spawn('python', ['script2.py']);
 // collect data from script
 python.stdout.on('data', function (data) {
  console.log('Pipe data from python script ...');
  largeDataSet.push(data);
 });
 // in close event we are sure that stream is from child process is closed
 python.on('close', (code) => {
 console.log(`child process close all stdio with code ${code}`);
 // send data to browser
 res.send(largeDataSet.join(""))
 });
 
})
app.listen(port, () => console.log(`Example app listening on port 
${port}!`))