Using python to build web applications

Question

This is a follow-up to two questions I asked a week or so back. The upshot of those was that I was building a prototype of an AI-based application for the web, and I wondered what language(s) to use. The conclusion seemed to be that I should go for something like python and then convert any critical bits into something faster like Java or C/C++.

That sounds fine to me, but I'm wondering now whether python is really the right language to use for building a web application. Most web applications I've worked on in the past were C/C++ CGI and then php. The php I found much easier to work with as it made linking the user interface to the back-end so much easier, and also it made more logical sense to me.

I've not used python before, but what I'm basically wondering is how easy is CGI programming in python? Will I have to go back to the tedious way of doing it in C/C++ where you have to store HTML code in templates and have the CGI read them in and replace special codes with appropriate values or is it possible to have the templates be the code as with php?

I'm probably asking a deeply ignorant question here, for which I apologise, but hopefully someone will know what I'm getting at! My overall question is: is writing web applications in python a good idea, and is it as easy as it is with php?

Answer 1

Python is a good choice.

I would avoid the CGI model though - you'll pay a large penalty for the interpreter launch on each request. Most Python web frameworks support the WSGI standard and can be hooked up to servers in a myriad of ways, but most live in some sort of long-running process that the web server communicates with (via proxying, FastCGI, SCGI, etc).

Speaking of frameworks, the Python landscape is ripe with them. This is both good and bad. There are many fine options but it can be daunting to a newcomer.

If you are looking for something that comes prepackaged with web/DB/templating integration I'd suggest looking at Django, TurboGears or Pylons. If you want to have more control over the individual components, look at CherryPy, Colubrid or web.py.

As for whether or not it is as "easy as PHP", that is subjective. Usually it is encouraged to keep your templates and application logic separate in the Python web programming world, which can make your life easier. On the other hand, being able to write all of the code for a page in a PHP file is another definition of "easy".

Good luck.

Answer 2

"how easy is CGI programming in python?" Easier than C, that's for sure. Python is easier because -- simply -- it's an easier language to work with than C. First and foremost: no memory allocation-deallocation. Beyond that, the OO programming model is excellent.

Beyond the essential language simplicity, the Python WSGI standard is much easier to cope with than the CGI standard.

However, raw CGI is a huge pain when compared with the greatly simplified world of an all-Python framework (TurboGears, CherryPy, Django, whatever.)

The frameworks impose a lot of (necessary) structure. The out-of-the-box experience for a CGI programmer is that it's too much to learn. True. All new things are too much to learn. However, the value far exceeds the investment.

With Django, you're up and running within minutes. Seriously. django-admin.py startproject and you have something you can run almost immediately. You do have to design your URL's, write view functions and design page templates. All of which is work. But it's less work than CGI in C.

Django has a better architecture than PHP because the presentation templates are completely separated from the processing. This leads to some confusion (see Syntax error whenever I put python code inside a django template) when you want to use the free-and-unconstrained PHP style on the Django framework.

linking the user interface to the back-end

Python front-end (Django, for example) uses Python view functions. Those view functions can contain any Python code at all. That includes, if necessary, modules written in C and callable from Python.

That means you can compile a CLIPS module with a Python-friendly interface. It becomes something available to your Python code with the import statement.

Sometimes, however, that's ineffective because your Django pages are waiting for the CLIPS engine to finish. An alternative is to use something like a named pipe.

You have your CLIPS-based app, written entirely in C, reading from a named pipe. Your Django application, written entirely in Python, writes to that named pipe. Since you've got two independent processes, you'll max out all of your cores pretty quickly like this.