How to call python script from NodeJs

Question

I need to call this python script in NodeJs.

Read.py

#!/usr/bin/env python
# -*- coding: utf8 -*-

import RPi.GPIO as GPIO
import MFRC522
import signal

continue_reading = True

# Capture SIGINT for cleanup when the script is aborted
def end_read(signal,frame):
    global continue_reading
    print "Ctrl+C captured, ending read."
    continue_reading = False
    GPIO.cleanup()

# Hook the SIGINT
signal.signal(signal.SIGINT, end_read)

# Create an object of the class MFRC522
MIFAREReader = MFRC522.MFRC522()

# Welcome message
print "Welcome to the MFRC522 data read example"
print "Press Ctrl-C to stop."

# This loop keeps checking for chips. If one is near it will get the UID and authenticate
while continue_reading:

    # Scan for cards    
    (status,TagType) = MIFAREReader.MFRC522_Request(MIFAREReader.PICC_REQIDL)

    # If a card is found
    if status == MIFAREReader.MI_OK:
    # Get the UID of the card
    (status,uid) = MIFAREReader.MFRC522_Anticoll()

    # If we have the UID, continue
    if status == MIFAREReader.MI_OK:

        # Print UID
        print "Card read UID: "+str(uid[0])+","+str(uid[1])+","+str(uid[2])+","+str(uid[3])

        # This is the default key for authentication
        key = [0xFF,0xFF,0xFF,0xFF,0xFF,0xFF]

        # Select the scanned tag
        MIFAREReader.MFRC522_SelectTag(uid)

        # Authenticate
        status = MIFAREReader.MFRC522_Auth(MIFAREReader.PICC_AUTHENT1A, 8, key, uid)

        # Check if authenticated
        if status == MIFAREReader.MI_OK:
            MIFAREReader.MFRC522_Read(8)
            MIFAREReader.MFRC522_StopCrypto1()
        else:
            print "Authentication error"

I used python-shell, here is the NodeJs code for that

Test.js

var PythonShell = require('python-shell');

var options = {
scriptPath: '/home/pi/gpio-admin/MFRC522-python/'
};
var pyshell = new PythonShell('Read.py',options);


pyshell.on('message', function (message) {

    console.log(message);
});

But when I ran this code I didn't see anything in Node side. I think problem occurs when python script comes to this level.

   (status,TagType) = MIFAREReader.MFRC522_Request(MIFAREReader.PICC_REQIDL)

Because I just ran with while loop which has only print statement then it works. After that I tried another way to achieve this. But I got same problem which I have with above.Here is another method

AltTest.js

var python = require('child_process').spawn(
 'python',
 // second argument is array of parameters, e.g.:
 ["/home/pi/gpio-admin/MFRC522-python/Read.py"]
 );
 var output = "";
 python.stdout.on('data', function(){ 

    output += data ;
    console.log(data);
});
 python.on('close', function(code){ 

   console.log("Here you are there...");
 });

Any help would be appreciated

Answer 1

My node js code

const { spawn }=require('child_process')

const child_python=spawn('python',['hello.py']);

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

child_python.stderr.on('data',(data)=>{
    console.log(`stderr : ${data}`);
})

child_python.on('close',(code)=>{
    console.log(`child process exited with code ${code}`)
})

You can check this video to run your Python script from Nodejs It tells how to pass arguments also

Link https://www.youtube.com/watch?v=eN0nMuS8ur8

Answer 2

If you like to avoid package managers / bloat, consider writing a shell script function to run the python, stream results locally to a txt file, collect and send on e.g. using http:

    const { exec } = require("child_process");
    
    function runShellScript(script, callback) {
        exec(script, (error, stdOut, stderr) => {
            
            var result = {status: true};
            
            if (error) {
                result.status = false;
                result.error = error.message;
            }
            if (stderr) {
                result.status = false;
                result.stderr = stderr;
            }
    
            if(stdOut){
                result.result = stdOut;
            }
            
    
            callback(result);
        });
    }
    
    runShellScript("python3 myscript.py >> output.txt", function(res) {
        console.log(res);
fs.readFileSync('output.txt');
    });

Answer 3

Well yoy can run python script from node.js in way like this. Use child_process.spawn (this is build in node.js library)

router.get('/', (req, res) => {
    const {spawn} = require('child_process');
    const path = require('path');
    function runScript(){
        return spawn('python', [
              path.join(__dirname, '../../scripts/myscript.py'),
              '-some_arg',
              '--another_arg',
        ]);
    }
    const subprocess = runScript();
    // print output of script
    subprocess.stdout.on('data', (data) => {
            console.log(`data:${data}`);
    });
    subprocess.stderr.on('data', (data) => {
           console.log(`error:${data}`);
    });
    subprocess.stderr.on('close', () => {
               console.log("Closed");
    });
    // const subprocess = runScript()
    res.set('Content-Type', 'text/plain');
    subprocess.stdout.pipe(res);
    subprocess.stderr.pipe(res);
});

Answer 4

Adopt a micro-services approach. Host the Python script as a HTTP REST API service. Consume the API from node.js - you do not need to integrate the technologies; it's not scalable.

Answer 5

• install python-shell :- npm install python-shell

  Index.js

  let {PythonShell} = require('python-shell')
  
  function runPy(){
      return new Promise(async function(resolve, reject){
            let options = {
            mode: 'text',
            pythonOptions: ['-u'],
            scriptPath: './test.py',//Path to your script
            args: [JSON.stringify({"name": ["xyz", "abc"], "age": ["28","26"]})]//Approach to send JSON as when I tried 'json' in mode I was getting error.
           };
  
            await PythonShell.run('test.py', options, function (err, results) {
            //On 'results' we get list of strings of all print done in your py scripts sequentially. 
            if (err) throw err;
            console.log('results: ');
            for(let i of results){
                  console.log(i, "---->", typeof i)
            }
        resolve(results[1])//I returned only JSON(Stringified) out of all string I got from py script
       });
     })
   } 
  
  function runMain(){
      return new Promise(async function(resolve, reject){
          let r =  await runPy()
          console.log(JSON.parse(JSON.stringify(r.toString())), "Done...!@")//Approach to parse string to JSON.
      })
   }
  
  runMain() //run main function
  

test.py

    import sys #You will get input from node in sys.argv(list)
    import json
    import pandas as pd #Import just to check if you dont have pandas module you can comment it or install pandas using pip install pandas

    def add_two(a, b):
        sum = 0
        for i in range(a, b):
            sum += i
        print(sum)  

    if __name__ == "__main__":
        print("Here...!")
        # print(sys.argv)
        j = json.loads(sys.argv[1]) #sys.argv[0] is filename
        print(j)
        add_two(20000, 5000000) #I make this function just to check 
    # So for all print done here you will get a list for all print in node, here-> console.log(i, "---->", typeof i)

Answer 6

There are multiple ways of doing this.

• first way is by doing npm install python-shell

and here's the code

var PythonShell = require('python-shell');
//you can use error handling to see if there are any errors
PythonShell.run('my_script.py', options, function (err, results) { 
//your code

you can send a message to python shell using pyshell.send('hello');

you can find the API reference here- https://github.com/extrabacon/python-shell

• second way - another package you can refer to is node python , you have to do npm install node-python

• third way - you can refer to this question where you can find an example of using a child process- How to invoke external scripts/programs from node.js

a few more references - https://www.npmjs.com/package/python

if you want to use service-oriented architecture - http://ianhinsdale.com/code/2013/12/08/communicating-between-nodejs-and-python/