Why does PHP just work with Ajax but Python doesn't?

Question

Building a PHP script that responds to an Ajax request is as easy as:

<?php
  $command = $_POST["command"];
  if ($command == "say_hello") {
    $name = $_POST["name"];
    echo json_encode(array("message" => "Hello, " . $name));
  }
?>

and, at least if you're using jQuery on the client side, and if you specified a callback function on the original request, the array containing the message will be passed into that callback function.

But with Python it's not that simple. Or at least I haven't figured out how to make it that simple. If I just try to "print" a response (paralleling PHP's "echo" statement above) the client doesn't get anything back.

Whenever I've looked on the internet for how to respond to an Ajax request with Python, the answer always involves using Django or some other web framework.

And I know those things are great, but what is PHP doing that makes using a similar package unnecessary? I would like to be writing my server-side script in Python instead of PHP, but I'd prefer a D.I.Y. approach to using a third-party framework for what should be (right?) a pretty simple task.

Any help? An example of how to do this would be much appreciated.

Answer 1

But with Python it's not that simple. Or at least I haven't figured out how to make it that simple. If I just try to "print" a response (paralleling PHP's "echo" statement above) the client doesn't get anything back.

I might have some of the details wrong, but I'll try to explain why this is the case. Firstly, the PHP you're talking about is baked directly into the apache webserver. When you do an echo, it outputs the result to the response stream (a TCP connection between the server and client). When you do print in python, what you're doing is outputting the result to standard out (the command line).

How most languages work with the web, is that a request comes in to some kind of web server, and that web server executes a program. The program is responsible for returning a stream, which the webserver takes, and streams to the client over the TCP connection.

I'm assuming that the webserver redirects PHPs standard out to the webservers stream, and that is how PHP is able to use echo to return its result. This is the exception, not the rule.

So, to use python to serve requests, you need to have a webserver that can execute python in some way. This is traditionally done using CGI. More recently, something like mod_python was used to host the python within apache. Nowadays, wsgi or mod_wsgi is used, which is the standard defined for webservers talking to python.

You might want to look at something like web.py, which is a minimalist python web framework. This will get you very very close to what you're trying to do.

Answer 2

PHP was built with the web in mind from the very beginning. In contrast Python was designed as a general purpose language.

When you echo from PHP you're actually writing to a stream that is sent to the user as part of an HTTP response. When you do a print in python the output, by default, is written to the stdout stream which means instead of being sent to the user over http the output is written to the console (or whatever is capturing stdout at the moment).

So to PHP, HTTP is a first class citizen. To more general purpose languages like Python, Ruby, Erlang, C, C++, and so many other languages. You have to communicate to HTTP in different ways. PHP already handles that communication through apache's mod_php or through something like PHP-FPM.

Sooo....

As far as creating your own server side script, I'd highly suggest against it as Python's Frameworks take the place of the layer that PHP is built on. So creating a standards compliant http server on your own with Python isn't going to be very simple. The reason that this is so hard is that you'd either have to interface with CGI or WSGI (a Python standard for dealing with the web) or create your own HTTP server. If you think you're up to the task then I highly suggest it! You'd probably learn a whole lot by doing it, but it isn't going to be the easiest thing. The great thing is that so many libraries already take care of this communication for you. For example, if you're looking for something lightweight, I highly suggest a micro-framework like flask which is one I personally use if I need something very simple. It is much easier to get started than django, but it also has less batteries included.

Hope this helps!