Python & XML

The BillSummary Example

To pull together some of the validation techniques presented in this chapter, we develop an example application that utilizes a DTD, flat-file conversion, and XML validation.

In the following set of programs, we develop an Internet system that parses a flat file submitted by a web browser, converts the flat text to XML, validates the XML, stores the XML to disk under a unique ID for publishing, and communicates success or failure back to the browser (or HTTP) client. Such an arrangement can act as an HTTP-based interface for converting flat files to XML (and making the resultant XML files available over HTTP) in a distributed system.

To accomplish this, use Python’s CGI libraries to grab a flat file from an HTTP request. Use string and file APIs to parse the flat file submitted by the browser, and a DOM implementation to construct a document object based on the flat file’s contents. A validating parser is used to ensure that the constructed DOM faithfully adheres to the established Bill Summary DTD.

All of the files for this example are available as part of the examples archive.

The files used in this example should be placed in a CGI-capable directory on your web server. In this section, we create the following files:

flatfile.html

Allows you to send the flat file to CGI script using a browser. BillSummary.txt, the flat file, is preloaded as the form submission.

FlatfileParser.py

A class that parses the flat file and returns a DOM document.

ValidityError.py