A Web-Based Lunch Ordering System
Maybe this article should be entitled “How I Discovered Python and Ditched Everything Else”, instead. I have always wanted to write web-based applications but somehow found that getting started was quite intimidating. So, having procrastinated for years, I finally got around to writing my first application. My work required an intra-office application for which some values needed prompting on a web page. These values are sent to a CGI script, cross-verified via an SQL database, dispatched to a waiting process via sockets, and the results sent back to the web page.
By luck, I stumbled upon a scripting language called Python. I was reading a recent issue of Linux Journal (December 1999), in which they interviewed Eric Raymond, who mentioned that he now programs only in Python. At that point, I was a day into implementing the above system in Perl and was not quite finished. If Python was good enough for Eric, it was worth a try.
Well, I finished what I wanted to do in just over two hours. This was using a language that I had not heard of two hours earlier. At the risk of losing my professional advantage, I thought I would share with others how easy Python is to use, especially to do CGI (and almost everything else). As the above application would be too technical and boring to actually work through (and I'd probably get sued by my employers), I've decided to work through another, much more interesting exercise.
Work being situated in a semi-remote location (culinary-wise, except for the place next door, which has excellent food but is a bit expensive to eat lunch at every day), take-out lunch was organised to be delivered to us once a week. Each participant took turns organised the lunch orders. Being spread out over three floors, it was quite a chore, and no one looked forward to doing it. A web-based ordering system seemed to me the obvious solution but not having done any CGI programming before, it seemed quite overwhelming. The others did not seem to care. But writing CGI web systems can be quite simple, especially when one can do it using Python. (Okay, Perl gurus may disagree, but that's the whole point, i.e., a Perl guru versus a Python novice!)
I knew roughly how I wanted it structured. There'd be a web page with a pull-down list with the restaurant menu, and, by clicking on a submit button, an e-mail with the person</#146>s order would be sent to the nominated lunch organiser.
Based on hearsay and some cursory research on the Net, I decided to use the following tools:
Python for the server side
Apache for the web server, which is distributed with Linux (well, it was with my copy of Red Hat Linux 6.2); there is also a Windows version, too, if one is so inclined
Linux for the web server OS
In designing the web pages, I decided to keep it fairly simple: a pull-down box with some radio buttons (see Figure 1).
I could have used some HTML editor but decided that I could not handle learning another new package, so I did it by hand. Since what I wanted to do wasn't complicated, the by-hand method proved sufficient.
It was easy to install the web server using Linux. When I was installing Linux, the option to install Apache was ticked. When I typed in localhost as the URL to Netscape, it displayed the Apache page with the message that if I saw that page, everything was A-Okay! Whoo-hooo... so far so good. (See http://www.apache.org/ for more details). You'll probably need to be root (the superuser) to do the install.
The most tricky lines would be the ON-SUBMIT statement:
<FORM NAME="order" onSubmit="return Validate();" ACTION="http://localhost/cgi-bin/lunch.cgi" METHOD="POST">
There are two ways a web page can communicate with a CGI script: GET and POST. In a nutshell, GET sends the information as part of the URL (i.e., you might have seen some URLs which resemble http://localhost/script.cgi?param1=value1¶m2=value2 in your surfing of the Internet). When POST is used, the form information is sent via the standard input, i.e., the CGI script needs to read in standard input, and then parse the input separate out the various parameters.
It is generally accepted that POST is better (more robust, not limited by the maximum character limit of shell used). The methods used to extract the data differ according to whether POST or GET is used, but Python hides this from you (which is good).
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