CODEWITHSUNDEEP
pythonnode.js
Ramzan
Ramzan

Reputation: 71

How to run a Python script in Node.js synchronously?

I am running the following Python script in Node.js through python-shell:

import sys
import time
 x=0
 completeData = "";
 while x<800:
  crgb =  ""+x;
  print crgb
  completeData = completeData + crgb + "@";
  time.sleep(.0001)
  x = x+1
  file = open("sensorData.txt", "w")
  file.write(completeData)
  file.close()
  sys.stdout.flush()
else:
 print "Device not found\n"

And my corresponding Node.js code is:

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

PythonShell.run('sensor.py', function (err) {
    if (err) throw err;
    console.log('finished');
});
console.log ("Now reading data");

Output is:

Now reading data
finished

But expected output is:

finished 
Now reading data

Node.js can not execute my Python script synchronously, it executes first all the code following the PythonShell.run function then executes PythonShell.run. How can I execute first PythonShell.run then the following code? Any help will be mostly appreciated... It is an emergency please!

Upvotes: 6

Views: 5486

Answers (4)

Diarex
Diarex

Reputation: 39

It work for me:

let {PythonShell} = require('python-shell');

var options = {
    mode:           'text',
    pythonPath:     'python',
    pythonOptions:  [],
    scriptPath:     '',
    args:           []
};

async function runTest()
{
    const { success, err = '', results } = await new Promise(
        (resolve, reject) =>
        {
            PythonShell.run('hello.py', options,
                function (err, results)
                {
                    if (err)
                    {
                        reject({ success: false, err });
                    }

                    console.log('PythonShell results: %j', results);

                    resolve({ success: true, results });
                }
            );
        }
    );

    console.log("python call ends");

    if (! success)
    {
        console.log("Test Error: " + err);
        return;
    }

    console.log("The result is: " + results);

    // My code here

    console.log("end runTest()");
}

console.log('start ...');

runTest();

console.log('... end main');

The result is:

start ...
... end main
PythonShell results: ["Hello World!"]
python call ends
The result is: Hello World!
end runTest()

Upvotes: 3

Enrique Ruiz
Enrique Ruiz

Reputation: 11

I had the same problem and resolved it by making a promise with the PythonShell.run method inside it. Then, you only have to await that promise and your code runs synchronously.

The promisify method:

RunPythonScript: function(scriptPath, args, pythonFile){
  let options = {
    mode: 'text',
    pythonPath: 'python',
    pythonOptions: [], 
    scriptPath: scriptPath,
    args: args,
  };

  return new Promise((resolve,reject) =>{
    try{
      PythonShell.run(pythonFile, options, function(err, results) {
        if (err) {console.log(err);}
        // results is an array consisting of messages collected during execution
        console.log('results', results);
        resolve();          
      }); 
    }
    catch{
      console.log('error running python code')
      reject();
    }
  })
},

Then, you await the promise:

await RunPythonScript(YOURscriptPath,YOURargsScript,YOURpythonFile);

Upvotes: 1

Tarzi
Tarzi

Reputation: 1

export default {
    data () {
            return {
            }
        },
        method: {
            callfunction () {
              console.log ("Now reading data");
            },
            pyth (){
              var PythonShell = require('python-shell');
              var vm = this; //save the object (this) in variable vm to use inside pythonshell.run
              PythonShell.run('sensor.py', function (err) {
                  if (err) throw err;
                  console.log('finished');
                  vm.callfunction();
              });
              
            }
        }
}

Upvotes: -1

Jean-Fran&#231;ois Fabre
Jean-Fran&#231;ois Fabre

Reputation: 140256

As this is asynchronous, add an end callback (found in the documentation) instead of instructions at top level

// end the input stream and allow the process to exit 
pyshell.end(function (err) {
  if (err) throw err;
  console.log ("Now reading data");
});

Upvotes: 0

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