Use ajax to call php, to call python, and get the result

I have built a website with a fairly complex structure and lots of javascript and php functions. I avoided jquery to make it lighter.

I now want to add a python function that should return a value to it. Most people recommend Flask for this, but all the examples I have found seem to require re-arranging the index page etc, which I don’t want to do (but please correct me if I am misunderstanding that).

So, the simple solution I thought about is to use ajax to call a php script, which in turn executes a python file. The problem, is that ajax isn’t waiting for the python script to complete and return the result.

I am mostly self-taught, so maybe what I did is all wrong, and any suggestion for a simple fix is much appreciated. Again, I’d like to avoid jquery and any major re-arrangement of pages etc.

Here is my code.

The ajax function that I use for lots of things on the site:

 var ajaxResponseText = "";//a global variable that I use to get back the results of PHP functions
function ajaxRequestReturn(phpRequest, vars, isAsync=false, setHeader=false, jsonParsed=true){
  ajaxResponseText = "";
  var req = new XMLHttpRequest();
  req.open("POST", phpRequest, isAsync);//not asynchronous
  if(setHeader){
    req.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
  }
  req.onProgress = function(){
    console.log("READYSTATE: ", req.readyState );
  }
  req.onload = function(){
    if(this.status==200){
      console.log("READYSTATE: ", this.readyState);
      console.log("responseText: ", this.responseText);
      if(jsonParsed){
        ajaxResponseText = JSON.parse(this.responseText);
      }else{
        ajaxResponseText = this.responseText;//php functions will echo a json array
      }
      // console.log(ajaxResponseText);
    }else if(this.status==404){
      ajaxResponseText = "Not found";
    }
  }
  req.onerror = function(){
    throw new Error("Bad request.");//this will stop the script and report the error
  }
  req.send(vars);
}

An event handler on the page calls:

ajaxRequestReturn("myPhpPythonCaller.php", vars="", isAsync=false, setHeader=false, jsonParsed=false)

myPhpPythonCaller.php simply has:

echo exec("pathToMyPythonEnv .venv/bin/python3 pathToMyPythonScript.py");

And the python script would produce and then print the result, say

from library import functionx

res = functionx()

print(res)

This set-up works for simple functions (e.g. print("hello") from MyPythonScript.py sends "hello" to ajaxResponseText, as expected ). However, if I call a function that takes time (I want to run an LLM, which would take dozens of seconds to produce an output), ajax doesn’t wait for the result, gets to status==200 and console.logs an empty ajaxResponseText.

What is the simplest, lightest way to do what I am trying to do?

Thank you so much for any tips!