mòine

mòine is a Python and Rust library for romanization-aware string comparison.

It implements Lattice Path Edit Distance (Kaji, 2023), a distance metric that compares strings through possible reading paths rather than only through visible surface characters.

This is useful when romanized input and written Japanese or Chinese look far apart as strings, but stay close in reading space.

>>> import moine

>>> moine.distance("moine", "モイニャ", lang="ja")
2

>>> moine.distance("もいにゃ", "モイニャ", lang="ja")
0

>>> moine.distance("weishiji", "威士忌", lang="zh")
0

>>> moine.distance("布納哈奔", "布納哈本", lang="zh")
0

The project is inspired by Nobuhiro Kaji's EMNLP 2023 Industry Track paper, "Lattice Path Edit Distance: A Romanization-aware Edit Distance for Extracting Misspelling-Correction Pairs from Japanese Search Query Logs".

Name

The project name comes from Moine, a peated malt from Bunnahabhain and one of the developer's favorite Scotch whiskies. In Japanese, the name has several plausible katakana renderings, such as モイニャ, モーイン, and モアンヌ, which makes it a fitting name for a project about readings, spelling variation, and ambiguity in input sequences.

Features

• Japanese comparison with UniDic-CWJ-derived reading artifacts.
• Chinese comparison with CC-CEDICT-derived no-tone pinyin artifacts.
• Plain string Levenshtein-compatible distance helpers.
• Lattice-aware Damerau-Levenshtein distance for adjacent transpositions.
• Normalized similarity / ratio helpers in 0.0..=1.0.
• RapidFuzz-inspired APIs such as cdist and partial matching helpers.

When To Use

mòine is best used after another system has produced candidates: lexical retrieval, n-gram search, BM25, embeddings, a product catalog, or an entity list. Use mòine to rescore those candidates in reading space.

Installation

Install the Python package:

pip install moine
uv pip install moine

Install the Rust command-line tool:

cargo install moine

The packages do not bundle dictionary data. Download the language artifacts you need explicitly:

uv run python -m moine download ja
uv run python -m moine download zh

moine download ja
moine download zh

Quick Start

Use the top-level Python API when you want mòine to load the default dictionary for a language:

import moine

print(moine.distance("もいにゃ", "モイニャ", lang="ja"))  # 0
print(moine.ratio("ピィート", "ピート", lang="ja"))  # 0.7142857142857143
print(moine.partial_ratio("ウイスキー", "ういすきーをのんでいます", lang="ja"))  # 1.0
print(moine.distance("weishiji", "威士忌", lang="zh"))  # 0

Load a dictionary explicitly when you want to control startup cost or artifact location:

import moine

dictionary = moine.load_dict(lang="ja")
moine.set_default_dictionary(dictionary)

print(moine.distance("もいにゃ", "モイニャ", lang="ja"))  # 0

Use cdist for query-by-choice matrices:

import moine

scores = moine.cdist(
    ["もいにゃ", "ぴーと", "ピィート"],
    ["モイニャ", "ピート", "ピーと", "ピィート"],
    lang="ja",
    metric="damerau_distance",
    score_cutoff=1,
)

For search or entity matching, generate candidates with your existing system and use mòine as a reading-aware reranker:

import moine

query = "moine"
candidates = ["モイニャ", "モーイン", "モアンヌ", "ストイーシャ"]

scores = moine.cdist(
    [query],
    candidates,
    lang="ja",
    metric="distance",
)[0]

ranked = sorted(zip(candidates, scores), key=lambda item: item[1])
print(ranked)
# [('モイニャ', 2), ('モーイン', 2), ('モアンヌ', 3), ('ストイーシャ', 7)]

Score interpretation is intentionally simple: distance=0 means the best reading paths are identical, distance metrics are smaller-is-better, ratio and normalized_similarity are in 0.0..=1.0 and larger-is-better, and score_cutoff filters in the RapidFuzz style.

Command Line

Most users only need the public runtime commands:

moine download ja
moine download zh
moine list
moine where
moine compare --left "もいにゃ" --right "モイニャ" \
  --artifact-metadata /path/to/moine-unidic-cwj-202512/metadata.yaml
moine chinese-compare --left weishiji --right 威士忌 \
  --artifact-metadata /path/to/moine-cedict-20260520/metadata.yaml

The artifact bundle, verification, archive, and diagnostic commands are maintainer-facing tools for producing and checking release assets. They are documented in docs/development.md and docs/release_process.md.

Documentation

• Project documentation
• Installation
• Python usage
• API reference
• Rust usage
• Dictionary artifacts
• Browser demo
• Rust docs

Developer and maintainer notes live under docs/, starting with docs/development.md and docs/release_process.md. See CONTRIBUTING.md before opening pull requests.

How It Differs From RapidFuzz

RapidFuzz is the better fit when both inputs should be compared directly as surface strings and you need a broad set of highly optimized fuzzy-matching scorers. mòine focuses on a narrower problem: comparing strings through possible reading paths before edit distance is computed.

Limitations

• mòine does not reproduce the original paper's private search-query-log evaluation.
• Dictionary-backed comparison requires separately distributed dictionary artifacts.
• UniDic matching intentionally does not use MeCab/Viterbi costs.
• Chinese support is Mandarin pinyin only; it does not model Cantonese/Jyutping or non-Mandarin readings.
• processor, score_hint, NumPy dtype options, and worker parallelism are not part of the initial cdist API.

Reference

[!CAUTION] This project is not the official implementation by the paper author.

@inproceedings{kaji-2023-lattice,
    title = "Lattice Path Edit Distance: A {R}omanization-aware Edit Distance for Extracting Misspelling-Correction Pairs from {J}apanese Search Query Logs",
    author = "Kaji, Nobuhiro",
    editor = "Wang, Mingxuan  and
      Zitouni, Imed",
    booktitle = "Proceedings of the 2023 Conference on Empirical Methods in Natural Language Processing: Industry Track",
    month = dec,
    year = "2023",
    address = "Singapore",
    publisher = "Association for Computational Linguistics",
    url = "https://aclanthology.org/2023.emnlp-industry.24/",
    doi = "10.18653/v1/2023.emnlp-industry.24",
    pages = "233--242",
    abstract = "Edit distance has been successfully used to extract training data, i.e., misspelling-correction pairs, of spelling correction models from search query logs in languages including English. However, the success does not readily apply to Japanese, where misspellings are often dissimilar to correct spellings due to the romanization-based input methods. To address this problem, we introduce lattice path edit distance, which utilizes romanization lattices to efficiently consider all possible romanized forms of input strings. Empirical experiments using Japanese search query logs demonstrated that the lattice path edit distance outperformed baseline methods including the standard edit distance combined with an existing transliterator and morphological analyzer. A training data collection pipeline that uses the lattice path edit distance has been deployed in production at our search engine for over a year."
}

License

mòine source code is licensed under either MIT or Apache-2.0. See LICENSE-MIT and LICENSE-APACHE.

Dictionary data is separate. UniDic-derived and CC-CEDICT-derived artifacts carry their own license and attribution metadata, and should keep dictionary license information separate from the mòine source-code license. See THIRD_PARTY_NOTICES.md.