The python CGI scripts in this folder illustrate several aspects
of cgi programming, in increasing levels of sophistication.

Run 'em in the http://cs.marlboro.edu/code/python/brownian/ folder.

And see the source code by appending _html to the URL, 
e.g. random_walk.cgi_html .

All three use PIL, the Python Imaging library;
see http://www.pythonware.com/products/pil/ for the details.
Note that this library is not installed by default with python itself. 
To install it on ubuntu:
    $ apt-get install python-imaging
To install it on MacOS with macports
    $ port install py27-pil  # for python 2.7*

A number of the standard cgi python modules are used
to pull the HTTP data from the environment variables
and print them out in the correct HTTP header format.

A good starting place for the basic docs on all this is 
http://wiki.python.org/moin/CgiScripts

And a nice summary of python itself and its use in cgi can be found at
http://www.python.org/doc/essays/ppt/sd99east/sld001.htm

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 random_walk_0.cgi     Generate a simple dynamic image consisting of a
                       few lines, one of which is randomly placed.

 random_walk_1.cgi     Generate a more complex dynamic image
 		       illustrating a 2D random walk.  The color of
 		       the path also changes randomly.

 random_walk.cgi       All the bells and whistles : 
 		       Generate the same 2D random walk, but with

		        1) image options which can be set by the
  		           visitor in the URL,
  		           e.g. random_walk.cgi?steplength=20, and

			2) cookies that remember these options so that
			   once set, the persist for that visitor.

			The options which can be set are (width,
			height, steplength, maxsteps,
			colorchangeperstep). And they can be reset to
			their default values by passing ?default=1 in
			the URL.  See source code for the dtails.

			This file also has a description of some of
			the debugging tricks you can use for python cgi.

--------------------------------------------------------------------------

Jim Mahoney
Computer Science @ Marlboro College
cs.marlboro.edu
Sep 2012