Call Python function from JavaScript code

Question

I'd like to call a Python function from JavaScript code, because there isn't an alternative in JavaScript for doing what I want. Is this possible? Could you adjust the below snippet to work?

JavaScript code:

var tag = document.getElementsByTagName("p")[0];
text = tag.innerHTML;
// Here I would like to call the Python interpreter with Python function
arrOfStrings = openSomehowPythonInterpreter("~/pythoncode.py", "processParagraph(text)");

~/pythoncode.py contains functions using advanced libraries that don't have an easy to write equivalent in JavaScript:

import nltk # is not in JavaScript
def processParagraph(text):
  ...
  nltk calls
  ...
  return lst # returns a list of strings (will be converted to JavaScript array)

Solution 1

All you need is to make an ajax request to your pythoncode. You can do this with jquery http://api.jquery.com/jQuery.ajax/, or use just javascript

$.ajax({
  type: "POST",
  url: "~/pythoncode.py",
  data: { param: text}
}).done(function( o ) {
   // do something
});

Solution 2

From the document.getElementsByTagName I guess you are running the javascript in a browser.

The traditional way to expose functionality to javascript running in the browser is calling a remote URL using AJAX. The X in AJAX is for XML, but nowadays everybody uses JSON instead of XML.

For example, using jQuery you can do something like:

$.getJSON('http://example.com/your/webservice?param1=x&param2=y', 
    function(data, textStatus, jqXHR) {
        alert(data);
    }
)

You will need to implement a python webservice on the server side. For simple webservices I like to use Flask.

A typical implementation looks like:

@app.route("/your/webservice")
def my_webservice():
    return jsonify(result=some_function(**request.args)) 

You can run IronPython (kind of Python.Net) in the browser with silverlight, but I don't know if NLTK is available for IronPython.

Solution 3

Typically you would accomplish this using an ajax request that looks like

var xhr = new XMLHttpRequest();
xhr.open("GET", "pythoncode.py?text=" + text, true);
xhr.responseType = "JSON";
xhr.onload = function(e) {
  var arrOfStrings = JSON.parse(xhr.response);
}
xhr.send();

Solution 4

Communicating through processes

Example:

Python: This python code block should return random temperatures.

# sensor.py

import random, time
while True:
    time.sleep(random.random() * 5)  # wait 0 to 5 seconds
    temperature = (random.random() * 20) - 5  # -5 to 15
    print(temperature, flush=True, end='')

Javascript (Nodejs): Here we will need to spawn a new child process to run our python code and then get the printed output.

// temperature-listener.js

const { spawn } = require('child_process');
const temperatures = []; // Store readings

const sensor = spawn('python', ['sensor.py']);
sensor.stdout.on('data', function(data) {

    // convert Buffer object to Float
    temperatures.push(parseFloat(data));
    console.log(temperatures);
});

Solution 5

You cannot run .py files from JavaScript without the Python program like you cannot open .txt files without a text editor. But the whole thing becomes a breath with a help of a Web API Server (IIS in the example below).

1. Install python and create a sample file test.py

   import sys
   # print sys.argv[0] prints test.py
   # print sys.argv[1] prints your_var_1
   
   def hello():
       print "Hi" + " " + sys.argv[1]
   
   if __name__ == "__main__":
       hello()
   

2. Create a method in your Web API Server

   [HttpGet]
   public string SayHi(string id)
   {
       string fileName = HostingEnvironment.MapPath("~/Pyphon") + "\\" + "test.py";          
   
       Process p = new Process();
       p.StartInfo = new ProcessStartInfo(@"C:\Python27\python.exe", fileName + " " + id)
       {
           RedirectStandardOutput = true,
           UseShellExecute = false,
           CreateNoWindow = true
       };
       p.Start();
   
       return p.StandardOutput.ReadToEnd();                  
   }
   

3. And now for your JavaScript:

   function processSayingHi() {          
      var your_param = 'abc';
      $.ajax({
          url: '/api/your_controller_name/SayHi/' + your_param,
          type: 'GET',
          success: function (response) {
              console.log(response);
          },
          error: function (error) {
              console.log(error);
          }
       });
   }
   

Remember that your .py file won't run on your user's computer, but instead on the server.

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Comments

[Fred Foo]

No, browsers (fortunately) won't execute arbitrary Python code. You'll want to run that in a server.

[John Dvorak]

Javascript runs on the client. I assume the python runs on the server. You could send an ajax request to the server. It won't be fast.

[Asad Saeeduddin]

Using ajax, send text to a python script on your server. Set up the script to return data in an easy to parse (for js) notation (like JSON) and assign the result to arrOfStrings in the success handler.

[John Dvorak]

Also, finding a python engine for javascript won't be easy either

[Admin]

You can run the official Python interpreter in the browser by compiling it using clang and Emscripten. This has been done before.

[Paulo Scardine]

You can run IronPython (kind of Python.Net) in the browser with silverlight, but I don't know if NLTK is available for IronPython.

[SO_fix_the_vote_sorting_bug]

@FredFoo, What would actually be fortunate is if browsers didn't run ECMAScript (which is called JavaScript for rather dubious historical reasons.) What would also be fortunate is if browsers had been running a secure subset (which is what anyone means by running anything in a browser, your straw man notwithstanding) of Python since the '90s so we wouldn't have to be dealing with the current web mess.

[Extreme]

For those finding this on Google, checkout the modern answer here : stackoverflow.com/a/68497604/11173996

[xralf]

It looks interesting. Where could be the call of processParagraph(text) so that the return values ends in the variable arrOfStrings?

[xralf]

I'm running this code in firebug, but it logs []

[xralf]

OK, so how is it right? My Python file contains the correct function. Should I call the function in Python and the argument will be sys.argv[1]?

[NuclearPeon]

Could you elaborate? When calling a python function via ajax post, does it call the __ main __ method? Because main cannot return a string. Can we expect to get any return values back? Does the data attribute correspond to the **kwargs dictionary in python, so we must have a method that accepts that? Otherwise, how do we specify the function in the python module?

[Matteo]

Thanks for the answer, but in order for the python script to execute it has to be deployed by a web server that supports it via CGI or WSGI. Could you please include in your answer how to solve that problem?

[Matteo]

Oh I'd be very happy to edit your answer if I knew how to do that, I was hoping you could provide some advice, cause I'm getting this error XMLHttpRequest cannot load file:~/pythoncode.py. Cross origin requests are only supported for protocol schemes: http, data, chrome-extension, https, chrome-extension-resource and even though I understood what the problem is don't know how to solve it. Any useful pointer? Thanks a lot. (btw...chessheaven seems really awesome! I'll try it out for sure, good thing you put a cute girl in your profile picture ;))

[Gustavo6046]

@NuclearPeon I suspect it's actually Python CGI, so it would print, not return. :D