# Using python to create CGI scripts

In this document we will (eventually) explain how to create Python CGI scripts for use with NetPresenz and probably other Mac-based HTTP servers too. Since CGI scripts are AppleEvent servers on the mac we will also learn a little about general AppleEvent server programming and about applet debugging.

> Note that the current setup is very preliminary, and hence itis probably not wise to base your strategic products on the information in this document:-) In stead, play with the code here and join the pythonmac-sig, where we I would like to have a discussion on a real design for a Mac CGI framework (preferrably something that will make CGI scripts portable to unix and other platforms).

## AppleEvent servers

Since AppleEvent clients are easier to write and understand than servers you should probably read the section on Open Scripting clients in Python first.

Next, let us have a look at the AE Server framework, MiniAEFrame.py. This file contains two classes, `MiniApplication` and `AEServer`. MiniApplication is a tiny replacement for `FrameWork.Application`, suitable if your application does not need windows and such. AEServer is a bit of glue that does part of the appleevent decoding for you. You call `installaehandler` passing it the class and id (4-char strings) of the event you have a handler for and the handler callback routine. When the appleevent occurs your callback is called with the right arguments. For now, your argument names are the 4-char values used internally by Open Scripting, eventually there will be a translation similar to what the generated OSA client suites provide.

You can test AEServer by double-clicking it. It will react to the standard run/open/print/quit OSA commands. If it is running as a normal python script and you drag a file onto the interpreter the script will tell you what event it got.

## A Minimal CGI script

To try a CGI script you will first need a http server. I have used the shareware NetPresenz by Peter Lewis (don't forget to pay if you give it more than a test run!). Install your http server, and make sure that it can serve textual documents.

Next, let us have a look at our example CGI scripts. CGI scripts have to be applications, so we will have to make an applet as explained in example 2. Our applet code, cgitest.cgi.py is a rather minimal `execfile` statement. The reason for this is debugging: the real code is in realcgitest.py, and this way you do not have to run mkapplet again every time you change the code. Rename realcgitest.py to cgitest.cgi.py once you are satisfied that it works.

The resource file is not very special, with one exception: since we want to do our own appleevent handling we don't want the Python initialization code to create argc and argv for use, since this might gobble up any appleevents we are interested in. For this reason we have included a 'Popt' resource that disables the argv initialization. An easy way to create this resource is to drop the `.rsrc` file (or the finished applet, if you like) onto `EditPythonPrefs` and set the "no argv processing" option.

The code itself is actually not too complicated either. We install handlers for "open application" and "quit" (stolen from the test code in MiniAEFrame) and the `"WWW\275"/"sdoc"` event, the event sent on CGI execution. The cgi handler pretty-prints the CGI arguments in HTML and returns the whole string that is to be passed to the client. The actual parameters passed are explained in http://www.biap.com/datapig/mrwheat/cgi_params.html.

To test the script drop `cgitest.cgi.py` onto `mkapplet`, move the resulting `cgitest.cgi` to somewhere where it is reachable by NetPresenz, and point your web browser towards it.