How to use Python-shell

1. Purpose

Call Python code from Javascrip code that runs on Node.js. I also want Javascript code to receive the output of Python code and process the received data on Javascript.

2. Means

Use Python-shell. Click here for Python-shell source

3. Preferences and installation

Explains the preparation and installation method for using Python-shell. It is assumed that node.js and python are already installed.

environment ・ Ubuntu 18.04 on Raspberry pi4 (Docker) ・ Because. js v12.14.0 ・ Npm 6.13.4

3-1 Installation method

Install python-shell using npm.

python

root@24f85fb6fd69:/home# npm install python-shell
npm WARN [email protected] No description
npm WARN [email protected] No repository field.

+ [email protected]
updated 1 package and audited 103 packages in 2.37s
found 0 vulnerabilities

3-2 Usage example

Create a directory TEST and place test.js and sample.py with the following code.

/home/pi/test/test.js

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

//Create an instance of PythonShell, pyshell. The python file name to call from js is'sample.py'
var pyshell = new PythonShell('sample.py');  

//From js to python code'5'Is provided as input data
pyshell.send(5); 
 
//Data is passed from python to js after executing the python code.
//The data passed to python is stored in "data".
pyshell.on('message', function (data) {
  console.log(data);
});

/home/pi/test/sample.py

import sys
data = sys.stdin.readline()  #Get data from standard input
num=int(data)

def sum(a):
    return a+3

print(sum(num)) #print()The contents of are passed to js.

3-3 execution

/home/pi/test/

root@24f85fb6fd69:/home/test# node test.js  //test.Run js
8    //The result processed by python is passed to javascript and executed.

4 When sending JSON data to Javascript → Python

I tried according to Python-shell source, but JSON format error "unexpected token T in json at position 1" is output everywhere. It doesn't work and traces, but there seems to be little information about Python-shell. So, I tried to send JSON data from Javascript to Python via a JSON file created separately, and it worked.

The code is posted below.

/home/pi/test/test.js

  const PYPATH="sample.py"

  var {PythonShell} = require('python-shell');
  var pyshell = new PythonShell(PYPATH, { mode: 'text'}); //mode is "JSON]It is better to specify "text" instead.

 //(1-1)Store the brand data to be registered in the dictionary type array.
  var obj={
    stock_num: 2145,
    c_name:"ABC_COMPANY",
    eps:100
  }

  //(1-2)The dictionary type array is converted to JSON format.
  var jsondat = JSON.stringify( obj );

  //(1-3)If the file to write the above jsondat already exists, delete the file once.
  if (fs.existsSync(JSONFILEPATH)) fs.unlinkSync(JSONFILEPATH)  
  //(1-4)If the file to write the above jsondat already exists, delete the file once.
  fs.writeFileSync(JSONFILEPATH,jsondat) 


  //(2)Send empty data from js to python code. To launch python code
  pyshell.send(""); 

  //(4)Receive Python execution results
  pyshell.on('message',  function (data) {
          console.log(data)
          res.send({
          message: "success"   //The result of the operation performed by python is returned to the front end.
        })
      })

/home/pi/test/sample.py

import sys
import json

#(3-1)JSON file test.open json
f = open('test.json', 'r')
#(3-2)test.Read json data
json_dict = json.load(f)
#(3-3)JSON data json_dict key:'stoch_num'To access.
dat1=json_dict['stock_num']
print(dat1) #print contents python-Return to shell

/home/pi/test/test.json

{"stock_num":"2145","c_name":"ABC company","eps":"100"}