lunr

What it is and what it does

Lunr is a Python port of the JavaScript Lunr.js library, designed to provide full-text search capabilities without the overhead of a dedicated search server like Elasticsearch. It works by parsing a collection of documents (represented as dictionaries) and building an inverted index that enables fast text queries. The index is kept entirely in memory, making it suitable for prototyping, smaller applications, or situations where deploying a full-scale search infrastructure is impractical.

A key feature is interoperability with Lunr.js: you can build an index in Python and serialize it for use in a browser-based frontend, or vice versa. This is particularly useful for static documentation sites (like those built with MkDocs) where you want to pre-compute the search index on the backend to minimize startup time in the browser. The trade-off is that you must recreate or reload the index when your application starts, since it exists only in memory.

Use it for

• Add full-text search to a documentation site (e.g., MkDocs) by pre-indexing pages in Python and serving the serialized index to the frontend.
• Prototype a search feature for a web application before committing to Elasticsearch or another production search engine.
• Search a small-to-medium corpus of documents in a Python application without external dependencies or infrastructure.
• Build a backend search index that can be shared with a JavaScript frontend using the same Lunr.js format.
• Implement keyword-based retrieval in a data processing pipeline where documents are already in memory.

Worth the install?

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Install

lunr on PyPI

Before you install

Low friction: pure Python wheel with only two lightweight runtime dependencies (importlib-metadata and typing-extensions). Maintenance is aging—last release was 524 days ago—but the repository is active and not archived, with a recent commit on 2025-03-08.

License in practice

MIT license (permissive): you can use, modify, and distribute lunr freely in both open-source and commercial projects with minimal restrictions, provided you include the license notice.

Quickstart

pip install lunr

from lunr import lunr

documents = [
    {'id': 'a', 'title': 'Mr. Green kills Colonel Mustard', 'body': 'Mr. Green killed Colonel Mustard in the study with the candlestick.'},
    {'id': 'b', 'title': 'Plumb waters plant', 'body': 'Professor Plumb has a green plant in his study'}
]
idx = lunr(ref='id', fields=('title', 'body'), documents=documents)
results = idx.search('kill')

Package facts

Evidence: lunr-0.8.0-py3-none-any.whl

Tags

More Text Processing packages

See also pagefind-bin · llama-index · llama-index-retrievers-bm25 · pagefind · rank-bm25 · voyager · pygmars · tinysegmenter · PyStemmer · lightrag-hku