Solr is a search server using Lucene to perform full text searching on indexed data. The most interesting part is that Solr uses a REST XML/JSON/HTTP API to add, modify, delete and search data so it's quite easy to use. However Solr and Lucene are written in Java so some Java servlet hosting is "required" :) If you need something bigger than for example Sphinx you can check this project out (Solr is used by Digg or sourceforge).
Search smarter with Apache Solr, Part 1: Essential features and the Solr schema
Search smarter with Apache Solr, Part 2: Solr for the enterprise
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A simple Python script for Solr would look like this: For a simple schema like this: