Getting Started with Pyparsing

Paul McGuire

Copyright © 2007 O'Reilly Media, Inc.

October XX, 2007

Abstract

Need to extract data from a text file or a web page? Or do you want to make your application more flexible with user-defined commands or search strings? Do regular expressions and lex/yacc make your eyes blur and your brain hurt?

Pyparsing could be the solution. Pyparsing is a pure-Python class library that makes it easy to build recursive-descent parsers quickly. There is no need to handcraft your own parsing state machine. With pyparsing, you can quickly create HTML page scrapers, logfile data extractors, or complex data structure or command processors. This Short Cut shows you how!

"I need to analyze this logfile..."

"Just extract the data from this web page..."

"We need a simple input command processor..."

"Our source code needs to be migrated to the new API..."

Each of these everyday requests generates the same reflex response in any developer faced with them: "Oh, *&#$*!, not another parser!"

The task of parsing data from loosely formatted text crops up in different forms on a regular basis for most developers. Sometimes it is for one-off development utilities, such as the API-upgrade example, that are purely for internal use. Other times, the parsing task is a user-interface function to be built in to a command-driven application.

If you are working in Python, you can tackle many ...