How to call a Python function from Node js

Question

I have an Express Node js application  but I also have a machine learning algorithm to use in Python  Is there a way I can call Python functions from my Node js application to make use of the power of machine learning libraries

User · Answer

I m on node 10 and child process 1 0 2  The data from python is a byte array and has to be converted  Just another quick example of making a http request in python   node  const process   spawn  python     services request py    https   www google com     return new Promise  resolve  reject    gt       process stdout on  data   data   gt           resolve data toString         lt ------------ by default converts to utf-8            process stderr on  data   reject       request py  import urllib request import sys  def karl morrison is a pedant           response   urllib request urlopen sys argv 1       html   response read       print html      sys stdout flush    karl morrison is a pedant     p s  not a contrived example since node s http module doesn t load a few requests I need to make

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The Boa is good for your needs  see the example which extends Python tensorflow keras Sequential class in JavaScript  const fs   require  fs    const boa   require   pipcook boa    const   tuple  enumerate     boa builtins     const tf   boa import  tensorflow    const tfds   boa import  tensorflow datasets     const   keras     tf  const   layers     keras   const       train data  test data      info     tfds load  imdb reviews subwords8k   boa kwargs     split  tuple   tfds Split TRAIN  tfds Split TEST       with info  true    as supervised  true       const encoder   info features  text   encoder  const padded shapes   tuple       null    tuple         const train batches   train data shuffle 1000     padded batch 10  boa kwargs   padded shapes      const test batches   test data shuffle 1000     padded batch 10  boa kwargs   padded shapes       const embedding dim   16  const model   keras Sequential     layers Embedding encoder vocab size  embedding dim     layers GlobalAveragePooling1D      layers Dense 16  boa kwargs   activation   relu         layers Dense 1  boa kwargs   activation   sigmoid           model summary    model compile boa kwargs     optimizer   adam     loss   binary crossentropy     metrics     accuracy           The complete example is at  https   github com alibaba pipcook blob master example boa tf2 word-embedding js  I used Boa in another project Pipcook  which is to address the machine learning problems for JavaScript developers  we implemented ML DL models upon the Python ecosystem tensorflow keras pytorch  by the boa library

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The python-shell module by extrabacon is a simple way to run Python scripts from Node js with basic  but efficient inter-process communication and better error handling   Installation  npm install python-shell   Running a simple Python script   var PythonShell   require  python-shell     PythonShell run  my script py   function  err      if  err  throw err    console log  finished          Running a Python script with arguments and options   var PythonShell   require  python-shell     var options       mode   text     pythonPath   path to python     pythonOptions    -u      scriptPath   path to my scripts     args    value1    value2    value3       PythonShell run  my script py   options  function  err  results      if  err       throw err       Results is an array consisting of messages collected during execution   console log  results   j   results         For the full documentation and source code  check out https   github com extrabacon python-shell

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eslint-env es6     global require     global console   var express   require  express     var app   express        Creates a server which runs on port 3000 and      can be accessed through localhost 3000 app listen 3000  function          console log  server running on port 3000           app get   name   function req  res         console log  Running            Use child process spawn method from          child process module and assign it         to variable spawn      var spawn   require  child process   spawn            Parameters passed in spawn -         1  type of script         2  list containing Path of the script            and arguments for the script           E g   http   localhost 3000 name firstname Levente     var process   spawn  python    apiTest py                            req query firstname            Takes stdout data from script which executed         with arguments and send this data to res object     var output           process stdout on  data   function data             console log  Sending Info           res end data toString  utf8                  console log output          This worked for me  Your python exe must be added to you path variables for this code snippet  Also  make sure your python script is in your project folder

User · Answer

Most of previous answers call the success of the promise in the on  data    it is not the proper way to do it because if you receive a lot of data you will only get the first part  Instead you have to do it on the end event   const   spawn     require  child process    const pythonDir      dirname        pythonCode        Path of python script folder const python   pythonDir    pythonEnv bin python      Path of the Python interpreter      remove warning that you don t care about    function cleanWarning error        return error replace  Detector is not able to detect the language reliably  n g         function callPython scriptName  args        return new Promise function success  reject            const script   pythonDir   scriptName          const pyArgs    script  JSON stringify args            const pyprog   spawn python  pyArgs            let result               let resultError               pyprog stdout on  data   function data                result    data toString                         pyprog stderr on  data    data    gt                resultError    cleanWarning data toString                          pyprog stdout on  end   function                if resultError                          success JSON parse result                 else                  console error  Python error  you can reproduce the error with   n  python    script    pyArgs join                          const error   new Error resultError                   console error error                   reject resultError                                     module exports callPython   callPython    Call     const pythonCaller   require     core pythonCaller    const result   await pythonCaller callPython  preprocessorSentiment py     thekeyYouwant   value      python   try      argu   json loads sys argv 1   except      raise Exception  error while loading argument

User · Answer

Easiest way I know of is to use  child process  package which comes packaged with node   Then you can do something like   const spawn   require  child process   spawn  const pythonProcess   spawn  python    path to script py   arg1  arg2           Then all you have to do is make sure that you import sys in your python script  and then you can access arg1 using  sys argv 1   arg2 using  sys argv 2   and so on     To send data back to node just do the following in the python script   print dataToSendBack  sys stdout flush     And then node can listen for data using   pythonProcess stdout on  data    data    gt           Do something with the data returned from python script       Since this allows multiple arguments to be passed to a script using spawn  you can restructure a python script so that one of the arguments decides which function to call  and the other argument gets passed to that function  etc    Hope this was clear   Let me know if something needs clarification

User · Answer

You can now use RPC libraries that support Python and Javascript such as zerorpc  From their front page   Node js Client  var zerorpc   require  zerorpc     var client   new zerorpc Client    client connect  tcp   127 0 0 1 4242     client invoke  hello    RPC   function error  res  more        console log res         Python Server  import zerorpc  class HelloRPC object       def hello self  name           return  Hello   s    name  s   zerorpc Server HelloRPC    s bind  tcp   0 0 0 0 4242   s run

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You could take your python  transpile it  and then call it as if it were javascript  I have done this succesfully for screeps and even got it to run in the browser a la brython

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Example for people who are from Python background and want to integrate their machine learning model in the Node js application   It uses the child process core module   const express   require  express   const app   express    app get       req  res    gt         const   spawn     require  child process        const pyProg   spawn  python          pypy py          pyProg stdout on  data   function data             console log data toString             res write data           res end  end                app listen 4000       gt  console log  Application listening on port 4000       It doesn t require sys module in your Python script   Below is a more modular way of performing the task using Promise   const express   require  express   const app   express    let runPy   new Promise function success  nosuccess         const   spawn     require  child process        const pyprog   spawn  python          pypy py          pyprog stdout on  data   function data             success data                pyprog stderr on  data    data    gt             nosuccess data                app get       req  res    gt         res write  welcome n         runPy then function fromRunpy            console log fromRunpy toString             res end fromRunpy               app listen 4000       gt  console log  Application listening on port 4000

[python] How to call a Python function from Node.js

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