fast-langdetect 🚀

Overview

fast-langdetect is an ultra-fast and highly accurate language detection library based on FastText, a library developed by Facebook. Its incredible speed and accuracy make it 80x faster than conventional methods and deliver up to 95% accuracy.

• Supported Python 3.9 to 3.13.
• Works offline in low memory mode
• No numpy required (thanks to @dalf).

Background

This project builds upon zafercavdar/fasttext-langdetect with enhancements in packaging. For more information about the underlying model, see the official FastText documentation: Language Identification.

Possible memory usage

This library requires at least 200MB memory in low-memory mode.

Installation 💻

To install fast-langdetect, you can use either pip or pdm:

Using pip

pip install fast-langdetect

Using pdm

pdm add fast-langdetect

Usage 🖥️

In scenarios where accuracy is important, you should not rely on the detection results of small models, use low_memory=False to download larger models!

Prerequisites

• If the sample is too long or too short, the accuracy will be reduced.
• The model will be downloaded to system temporary directory by default. You can customize it by:
  • Setting FTLANG_CACHE environment variable
  • Using LangDetectConfig(cache_dir="your/path")

Native API (Recommended)

from fast_langdetect import detect, detect_multilingual, LangDetector, LangDetectConfig, DetectError

# Simple detection
print(detect("Hello, world!"))
# Output: {'lang': 'en', 'score': 0.12450417876243591}

# Using large model for better accuracy
print(detect("Hello, world!", low_memory=False))
# Output: {'lang': 'en', 'score': 0.98765432109876}

# Custom configuration with fallback mechanism
config = LangDetectConfig(
    cache_dir="/custom/cache/path",  # Custom model cache directory
    allow_fallback=True             # Enable fallback to small model if large model fails
)
detector = LangDetector(config)

try:
    result = detector.detect("Hello world", low_memory=False)
    print(result)  # {'lang': 'en', 'score': 0.98}
except DetectError as e:
    print(f"Detection failed: {e}")

# How to deal with multiline text
multiline_text = """
Hello, world!
This is a multiline text.
"""
multiline_text = multiline_text.replace("\n", " ")  
print(detect(multiline_text))
# Output: {'lang': 'en', 'score': 0.8509423136711121}

# Multi-language detection
results = detect_multilingual(
    "Hello 世界 こんにちは", 
    low_memory=False,  # Use large model for better accuracy
    k=3               # Return top 3 languages
)
print(results)
# Output: [
#     {'lang': 'ja', 'score': 0.4}, 
#     {'lang': 'zh', 'score': 0.3}, 
#     {'lang': 'en', 'score': 0.2}
# ]

Fallbacks

We provide a fallback mechanism: when allow_fallback=True, if the program fails to load the large model (low_memory=False), it will fall back to the offline small model to complete the prediction task.

# Disable fallback - will raise error if large model fails to load
# But fallback disabled when custom_model_path is not None, because its a custom model, we will directly use it.
import tempfile
config = LangDetectConfig(
    allow_fallback=False, 
    custom_model_path=None,
    cache_dir=tempfile.gettempdir(),
    )
detector = LangDetector(config)

try:
    result = detector.detect("Hello world", low_memory=False)
except DetectError as e:
    print("Model loading failed and fallback is disabled")

Convenient detect_language Function

from fast_langdetect import detect_language

# Single language detection
print(detect_language("Hello, world!"))
# Output: EN

print(detect_language("Привет, мир!"))
# Output: RU

print(detect_language("你好，世界！"))
# Output: ZH

Load Custom Models

# Load model from local file
config = LangDetectConfig(
    custom_model_path="/path/to/your/model.bin",  # Use local model file
    disable_verify=True                     # Skip MD5 verification
)
detector = LangDetector(config)
result = detector.detect("Hello world")

Splitting Text by Language 🌐

For text splitting based on language, please refer to the split-lang repository.

Benchmark 📊

For detailed benchmark results, refer to zafercavdar/fasttext-langdetect#benchmark.

References 📚

[1] A. Joulin, E. Grave, P. Bojanowski, T. Mikolov, Bag of Tricks for Efficient Text Classification

@article{joulin2016bag,
  title={Bag of Tricks for Efficient Text Classification},
  author={Joulin, Armand and Grave, Edouard and Bojanowski, Piotr and Mikolov, Tomas},
  journal={arXiv preprint arXiv:1607.01759},
  year={2016}
}

[2] A. Joulin, E. Grave, P. Bojanowski, M. Douze, H. Jégou, T. Mikolov, FastText.zip: Compressing text classification models

@article{joulin2016fasttext,
  title={FastText.zip: Compressing text classification models},
  author={Joulin, Armand and Grave, Edouard and Bojanowski, Piotr and Douze, Matthijs and J{\'e}gou, H{\'e}rve and Mikolov, Tomas},
  journal={arXiv preprint arXiv:1612.03651},
  year={2016}
}