sentencex

Sentence segmenter

A sentence segmentation library written in Rust language with wide language support optimized for speed and utility.

Bindings

Besides native Rust, bindings for the following programming languages are available:

Approach

If it’s a period, it ends a sentence.
If the preceding token is in the hand-compiled list of abbreviations, then it doesn’t end a sentence.

However, it is not ‘period’ for many languages. So we will use a list of known punctuations that can cause a sentence break in as many languages as possible.

We also collect a list of known, popular abbreviations in as many languages as possible.

Sometimes, it is very hard to get the segmentation correct. In such cases this library is opinionated and prefer not segmenting than wrong segmentation. If two sentences are accidentally together, that is ok. It is better than sentence being split in middle. Avoid over engineering to get everything linguistically 100% accurate.

This approach would be suitable for applications like text to speech, machine translation.

Consider this example: We make a good team, you and I. Did you see Albert I. Jones yesterday?

The accurate splitting of this sentence is ["We make a good team, you and I." ,"Did you see Albert I. Jones yesterday?"]

However, to achieve this level precision, complex rules need to be added and it could create side effects. Instead, if we just don’t segment between I. Did, it is ok for most of downstream applications.

The sentence segmentation in this library is non-destructive. This means, if the sentences are combined together, you can reconstruct the original text. Line breaks, punctuations and whitespaces are preserved in the output.

Usage

Rust

Install the library using

cargo add sentencex

Then, any text can be segmented as follows.

use sentencex::segment;

fn main() {
    let text = "The James Webb Space Telescope (JWST) is a space telescope specifically designed to conduct infrared astronomy. The U.S. National Aeronautics and Space Administration (NASA) led Webb's design and development.";
    let sentences = segment("en", text);

    for (i, sentence) in sentences.iter().enumerate() {
        println!("{}. {}", i + 1, sentence);
    }
}

The first argument is language code, second argument is text to segment. The segment method returns an array of identified sentences.

Python

Install from PyPI:

pip install sentencex

import sentencex

text = "The James Webb Space Telescope (JWST) is a space telescope specifically designed to conduct infrared astronomy. The U.S. National Aeronautics and Space Administration (NASA) led Webb's design and development."

# Segment text into sentences
sentences = sentencex.segment("en", text)
for i, sentence in enumerate(sentences, 1):
    print(f"{i}. {sentence}")

# Get sentence boundaries with indices
boundaries = sentencex.get_sentence_boundaries("en", text)
for boundary in boundaries:
    print(f"Sentence: '{boundary['text']}' (indices: {boundary['start_index']}-{boundary['end_index']})")

See bindings/python/example.py for more examples.

Node.js

Install from npm:

npm install sentencex

import { segment, get_sentence_boundaries } from 'sentencex';

const text = "The James Webb Space Telescope (JWST) is a space telescope specifically designed to conduct infrared astronomy. The U.S. National Aeronautics and Space Administration (NASA) led Webb's design and development.";

// Segment text into sentences
const sentences = segment("en", text);
sentences.forEach((sentence, i) => {
    console.log(`${i + 1}. ${sentence}`);
});

// Get sentence boundaries with indices
const boundaries = get_sentence_boundaries("en", text);
boundaries.forEach(boundary => {
    console.log(`Sentence: '${boundary.text}' (indices: ${boundary.start_index}-${boundary.end_index})`);
});

For CommonJS usage:

const { segment, get_sentence_boundaries } = require('sentencex');

See bindings/nodejs/example.js for more examples.

WebAssembly (Browser)

Install from npm:

npm install sentencex-wasm

or use a CDN like https://esm.sh/sentencex-wasm

import init, { segment, get_sentence_boundaries } from 'https://esm.sh/sentencex-wasm;

async function main() {
    // Initialize the WASM module
    await init();

    const text = "The James Webb Space Telescope (JWST) is a space telescope specifically designed to conduct infrared astronomy. The U.S. National Aeronautics and Space Administration (NASA) led Webb's design and development.";

    // Segment text into sentences
    const sentences = segment("en", text);
    sentences.forEach((sentence, i) => {
        console.log(`${i + 1}. ${sentence}`);
    });

    // Get sentence boundaries with indices
    const boundaries = get_sentence_boundaries("en", text);
    boundaries.forEach(boundary => {
        console.log(`Sentence: '${boundary.text}' (indices: ${boundary.start_index}-${boundary.end_index})`);
    });
}

main();

Language support

The aim is to support all languages where there is a wikipedia. Instead of falling back on English for languages not defined in the library, a fallback chain is used. The closest language which is defined in the library will be used. Fallbacks for ~244 languages are defined.

Performance

Following is a sample output of sentence segmenting The Complete Works of William Shakespeare. This file is 5.29MB. As you can see below, it took 178 milli second.

$ curl https://www.gutenberg.org/files/100/100-0.txt | ./target/release/sentencex -l en > /dev/null
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 5295k  100 5295k    0     0   630k      0  0:00:08  0:00:08 --:--:-- 1061k
Time taken for segment(): 178.745108ms
Total sentences: 150254

Measured on English Golden Rule Set (GRS) using mean F1 score across 60 test cases. List cases are excluded. The benchmark script is at benchmarks/compare.py and can be run with uv run benchmarks/compare.py.

The following libraries are compared:

mwtokenizer — Wikimedia rule-based tokenizer
blingfire — Microsoft’s fast tokenizer (C library)
nltk — Punkt sentence tokenizer
pysbd — Python port of pragmatic segmenter
spacy — dependency-parse based sentence segmentation
syntok — rule-based tokenizer

Tokenizer	English GRS F1 Score
sentencex	100.00
pysbd	93.00
blingfire	91.67
syntok	85.67
spacy	81.67
mwtokenizer	78.00
nltk	72.33

Thanks

https://github.com/diasks2/pragmatic_segmenter for test cases. The English golden rule set is also sourced from it.
https://github.com/mush42/tqsm for an earlier Rust port of this library.

License

MIT license. See License.txt

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