Problem: Get variable

[JohnnyCoffee]

I have a file (runwsgi.py) that starts the server with the intention of getting a variable from a form using an ajax. The problem that prints the value none? See the wsgi code below, because I can't find an error:

Ajax section :

    $('.btn').text('search').click(function() {
        // atribui valor a variavel
        var ws_search_field = $('.ws-search-field').val();
        // set method ajax:
        $.ajax({
            type : 'POST',
            url : 'runwsgi.py',
            data : { ws_search_field : ws_search_field },
            dataType : 'json',

Wsgi section :

import cgi

def apps(environ, ws_output):

    ws_mtd = environ['REQUEST_METHOD']

    ws_form = cgi.FieldStorage()
    ws_input = ws_form.getvalue('ws_search_field')

    if ws_mtd == 'POST':
        status = '200 OK'
        headers = [('Content-type', 'text/html; charset=utf-8')]
        ws_output(status, headers)
        return [str(ws_input).encode('utf-8')]

The output I get from the ws_search_field variable is: None
Note: Debugging in the chrome browser I see in the Form Data section it is possible to view the variable with the input value (ws_search_field: text)
Would there be an error to get the variable value in the code below?

ws_form = cgi.FieldStorage()
ws_input = ws_form.getvalue('ws_search_field')