Whoosh is a fast, featureful full-text indexing and searching library
implemented in pure Python. Programmers can use it to easily add search
functionality to their applications and websites. Every part of how Whoosh
works can be extended or replaced to meet your needs exactly.

Some of Whoosh's features include:

- Pythonic API.
- Pure-Python. No compilation or binary packages needed, no mysterious 
  crashes.
- Fielded indexing and search.
- Fast indexing and retrieval -- faster than any other pure-Python, scoring, 
  full-text search solution I know of.
- Pluggable scoring algorithm (including BM25F), text analysis, storage, 
  posting format, etc.
- Powerful query language.
- Pure Python spell-checker (as far as I know, the only one).

WWW: https://pypi.python.org/pypi/Whoosh
WWW: http://bitbucket.org/mchaput/whoosh