Call Python function from JavaScript code

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)

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
});

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.

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();

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);
});

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.

Despite what some replies and comments suggest, there are a number of ways for using Python on the front-end. For your question in particular, see this reply.