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15.2 CGI scripts

Unlike Webware servlets, which don't have to worry about the HTTP headers, CGI scripts must emit their own headers. To make a template CGI aware, add this at the top:

#extends Cheetah.Tools.CGITemplate
#implements respond
$cgiHeaders#slurp

Or if your template is inheriting from a Python class:

#extends MyPythonClass
#implements respond
$cgiHeaders#slurp

A sample Python class:

from Cheetah.Tools import CGITemplate
class MyPythonClass(CGITemplate):
    def cgiHeadersHook(self):
        return "Content-Type: text/html; charset=koi8-r\n\n"

Compile the template as usual, put the .py template module in your cgi-bin directory and give it execute permission. .cgiHeaders() is a ``smart'' method that outputs the headers if the module is called as a CGI script, or outputs nothing if not. Being ``called as a CGI script'' means the environmental variable REQUEST_METHOD exists and self.isControlledByWebKit is false. If you don't agree with that definition, override .isCgi() and provide your own.

The default header is a simple Content-type: text/html\n\n, which works with all CGI scripts. If you want to customize the headers (e.g., to specify the character set), override .cgiHeadersHook() and return a string containing all the headers. Don't forget to include the extra newline at the end of the string: the HTTP protocol requires this empty line to mark the end of the headers.

To read GET/POST variables from form input, use the .webInput() method (section 14.7), or extract them yourself using Python's cgi module or your own function. Although .webInput() was originally written for Webware servlets, it now handles CGI scripts too. There are a couple behavioral differences between CGI scripts and Webware servlets regarding input variables:

  1. CGI scripts, using Python's cgi module, believe REQUEST_METHOD and recognize either GET variables or POST variables, not both. Webware servlets, doing additional processing, ignore REQUEST_METHOD and recognize both, like PHP does.
  2. Webware servlets can ask for cookies or session variables instead of GET/POST variables, by passing the argument src='c' or src='s'. CGI scripts get a RuntimeError if they try to do this.

If you keep your .tmpl files in the same directory as your CGI scripts, make sure they don't have execute permission. Apache at least refuses to serve files in a ScriptAlias directory that don't have execute permission.

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