getting javascript form content with python

Thanks for the clarification in the comments. Since you are building a website, you'll want to use AJAX to call the python web application and return something (probably XML in your case, although I recommend reading about JSON). It sounds to me like you don't have the best solution to your problem yet, but that is another issue. I don't understand why you would go to the trouble of generating xml with python, reading it with JavaScript, updating it with JavaScript, and then reading it again with Python on form submission. For starters, think about what happens if your users disable JavaScript.

Anyways, I suggest reading about Flask and jQuery to get started. Your application might then look something like this in python:

from flask import Flask
app = Flask(__name__)

@app.route('/', methods=['POST', 'GET'])
def foo():
    if request.method == 'GET':
        # Generate the XML
        return myXML
    if request.method == 'POST':
        # Read that hidden field
        xml = request.form['the_hidden_xml']
        # Do what you will
        return render_template('homepage.html')

if __name__ == "__main__":
    app.run()

The JavaScipt probably does this:

function buildTheForm() {
    $.get('/', function(data) {
        // handle the xml in data
        alert('Load was performed.');
    });
}

The form probably does this:

<form action="/" method="post">

Is your system a web application, If so your javascript can post to python back-end using ajax. Then you can encrypt a form to json string and send to back-end, in back en you can parse that string into python variable... Javascript it self does not have access to your local file except you run it local (but it's really limitted)

I suggest you should try a web frame work like Django. It's easy to learn in one day.