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https://github.com/google/langextract

A Python library for extracting structured information from unstructured text using LLMs with precise source grounding and interactive visualization.
https://github.com/google/langextract

gemini gemini-ai gemini-api gemini-flash gemini-pro information-extration large-language-models llm nlp python structured-data

Last synced: about 2 months ago
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A Python library for extracting structured information from unstructured text using LLMs with precise source grounding and interactive visualization.

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README 

          


  

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# LangExtract



[![PyPI version](https://img.shields.io/pypi/v/langextract.svg)](https://pypi.org/project/langextract/)

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![Tests](https://github.com/google/langextract/actions/workflows/ci.yaml/badge.svg)



## Table of Contents



- [Introduction](#introduction)

- [Why LangExtract?](#why-langextract)

- [Quick Start](#quick-start)

- [Installation](#installation)

- [API Key Setup for Cloud Models](#api-key-setup-for-cloud-models)

- [Using OpenAI Models](#using-openai-models)

- [Using Local LLMs with Ollama](#using-local-llms-with-ollama)

- [More Examples](#more-examples)

  - [*Romeo and Juliet* Full Text Extraction](#romeo-and-juliet-full-text-extraction)

  - [Medication Extraction](#medication-extraction)

  - [Radiology Report Structuring: RadExtract](#radiology-report-structuring-radextract)

- [Contributing](#contributing)

- [Testing](#testing)

- [Disclaimer](#disclaimer)



## Introduction



LangExtract is a Python library that uses LLMs to extract structured information from unstructured text documents based on user-defined instructions. It processes materials such as clinical notes or reports, identifying and organizing key details while ensuring the extracted data corresponds to the source text.



## Why LangExtract?



1.  **Precise Source Grounding:** Maps every extraction to its exact location in the source text, enabling visual highlighting for easy traceability and verification.

2.  **Reliable Structured Outputs:** Enforces a consistent output schema based on your few-shot examples, leveraging controlled generation in supported models like Gemini to guarantee robust, structured results.

3.  **Optimized for Long Documents:** Overcomes the "needle-in-a-haystack" challenge of large document extraction by using an optimized strategy of text chunking, parallel processing, and multiple passes for higher recall.

4.  **Interactive Visualization:** Instantly generates a self-contained, interactive HTML file to visualize and review thousands of extracted entities in their original context.

5.  **Flexible LLM Support:** Supports your preferred models, from cloud-based LLMs like the Google Gemini family to local open-source models via the built-in Ollama interface.

6.  **Adaptable to Any Domain:** Define extraction tasks for any domain using just a few examples. LangExtract adapts to your needs without requiring any model fine-tuning.

7.  **Leverages LLM World Knowledge:** Utilize precise prompt wording and few-shot examples to influence how the extraction task may utilize LLM knowledge. The accuracy of any inferred information and its adherence to the task specification are contingent upon the selected LLM, the complexity of the task, the clarity of the prompt instructions, and the nature of the prompt examples.



## Quick Start



> **Note:** Using cloud-hosted models like Gemini requires an API key. See the [API Key Setup](#api-key-setup-for-cloud-models) section for instructions on how to get and configure your key.



Extract structured information with just a few lines of code.



### 1. Define Your Extraction Task



First, create a prompt that clearly describes what you want to extract. Then, provide a high-quality example to guide the model.



```python

import langextract as lx

import textwrap



# 1. Define the prompt and extraction rules

prompt = textwrap.dedent("""\

    Extract characters, emotions, and relationships in order of appearance.

    Use exact text for extractions. Do not paraphrase or overlap entities.

    Provide meaningful attributes for each entity to add context.""")



# 2. Provide a high-quality example to guide the model

examples = [

    lx.data.ExampleData(

        text="ROMEO. But soft! What light through yonder window breaks? It is the east, and Juliet is the sun.",

        extractions=[

            lx.data.Extraction(

                extraction_class="character",

                extraction_text="ROMEO",

                attributes={"emotional_state": "wonder"}

            ),

            lx.data.Extraction(

                extraction_class="emotion",

                extraction_text="But soft!",

                attributes={"feeling": "gentle awe"}

            ),

            lx.data.Extraction(

                extraction_class="relationship",

                extraction_text="Juliet is the sun",

                attributes={"type": "metaphor"}

            ),

        ]

    )

]

```



### 2. Run the Extraction



Provide your input text and the prompt materials to the `lx.extract` function.



```python

# The input text to be processed

input_text = "Lady Juliet gazed longingly at the stars, her heart aching for Romeo"



# Run the extraction

result = lx.extract(

    text_or_documents=input_text,

    prompt_description=prompt,

    examples=examples,

    model_id="gemini-2.5-flash",

)

```



> **Model Selection**: `gemini-2.5-flash` is the recommended default, offering an excellent balance of speed, cost, and quality. For highly complex tasks requiring deeper reasoning, `gemini-2.5-pro` may provide superior results. For large-scale or production use, a Tier 2 Gemini quota is suggested to increase throughput and avoid rate limits. See the [rate-limit documentation](https://ai.google.dev/gemini-api/docs/rate-limits#tier-2) for details.

>

> **Model Lifecycle**: Note that Gemini models have a lifecycle with defined retirement dates. Users should consult the [official model version documentation](https://cloud.google.com/vertex-ai/generative-ai/docs/learn/model-versions) to stay informed about the latest stable and legacy versions.



### 3. Visualize the Results



The extractions can be saved to a `.jsonl` file, a popular format for working with language model data. LangExtract can then generate an interactive HTML visualization from this file to review the entities in context.



```python

# Save the results to a JSONL file

lx.io.save_annotated_documents([result], output_name="extraction_results.jsonl", output_dir=".")



# Generate the visualization from the file

html_content = lx.visualize("extraction_results.jsonl")

with open("visualization.html", "w") as f:

    f.write(html_content)

```



This creates an animated and interactive HTML file:



![Romeo and Juliet Basic Visualization ](https://raw.githubusercontent.com/google/langextract/main/docs/_static/romeo_juliet_basic.gif)



> **Note on LLM Knowledge Utilization:** This example demonstrates extractions that stay close to the text evidence - extracting "longing" for Lady Juliet's emotional state and identifying "yearning" from "gazed longingly at the stars." The task could be modified to generate attributes that draw more heavily from the LLM's world knowledge (e.g., adding `"identity": "Capulet family daughter"` or `"literary_context": "tragic heroine"`). The balance between text-evidence and knowledge-inference is controlled by your prompt instructions and example attributes.



### Scaling to Longer Documents



For larger texts, you can process entire documents directly from URLs with parallel processing and enhanced sensitivity:



```python

# Process Romeo & Juliet directly from Project Gutenberg

result = lx.extract(

    text_or_documents="https://www.gutenberg.org/files/1513/1513-0.txt",

    prompt_description=prompt,

    examples=examples,

    model_id="gemini-2.5-flash",

    extraction_passes=3,    # Improves recall through multiple passes

    max_workers=20,         # Parallel processing for speed

    max_char_buffer=1000    # Smaller contexts for better accuracy

)

```



This approach can extract hundreds of entities from full novels while maintaining high accuracy. The interactive visualization seamlessly handles large result sets, making it easy to explore hundreds of entities from the output JSONL file. **[See the full *Romeo and Juliet* extraction example →](https://github.com/google/langextract/blob/main/docs/examples/longer_text_example.md)** for detailed results and performance insights.



## Installation



### From PyPI



```bash

pip install langextract

```



*Recommended for most users. For isolated environments, consider using a virtual environment:*



```bash

python -m venv langextract_env

source langextract_env/bin/activate  # On Windows: langextract_env\Scripts\activate

pip install langextract

```



### From Source



LangExtract uses modern Python packaging with `pyproject.toml` for dependency management:



*Installing with `-e` puts the package in development mode, allowing you to modify the code without reinstalling.*



```bash

git clone https://github.com/google/langextract.git

cd langextract



# For basic installation:

pip install -e .



# For development (includes linting tools):

pip install -e ".[dev]"



# For testing (includes pytest):

pip install -e ".[test]"

```



### Docker



```bash

docker build -t langextract .

docker run --rm -e LANGEXTRACT_API_KEY="your-api-key" langextract python your_script.py

```



## API Key Setup for Cloud Models



When using LangExtract with cloud-hosted models (like Gemini or OpenAI), you'll need to

set up an API key. On-device models don't require an API key. For developers

using local LLMs, LangExtract offers built-in support for Ollama and can be

extended to other third-party APIs by updating the inference endpoints.



### API Key Sources



Get API keys from:



*   [AI Studio](https://aistudio.google.com/app/apikey) for Gemini models

*   [Vertex AI](https://cloud.google.com/vertex-ai/generative-ai/docs/sdks/overview) for enterprise use

*   [OpenAI Platform](https://platform.openai.com/api-keys) for OpenAI models



### Setting up API key in your environment



**Option 1: Environment Variable**



```bash

export LANGEXTRACT_API_KEY="your-api-key-here"

```



**Option 2: .env File (Recommended)**



Add your API key to a `.env` file:



```bash

# Add API key to .env file

cat >> .env << 'EOF'

LANGEXTRACT_API_KEY=your-api-key-here

EOF



# Keep your API key secure

echo '.env' >> .gitignore

```



In your Python code:

```python

import langextract as lx



result = lx.extract(

    text_or_documents=input_text,

    prompt_description="Extract information...",

    examples=[...],

    model_id="gemini-2.5-flash"

)

```



**Option 3: Direct API Key (Not Recommended for Production)**



You can also provide the API key directly in your code, though this is not recommended for production use:



```python

result = lx.extract(

    text_or_documents=input_text,

    prompt_description="Extract information...",

    examples=[...],

    model_id="gemini-2.5-flash",

    api_key="your-api-key-here"  # Only use this for testing/development

)

```



## Using OpenAI Models



LangExtract supports OpenAI models (requires optional dependency: `pip install langextract[openai]`):



```python

import langextract as lx



result = lx.extract(

    text_or_documents=input_text,

    prompt_description=prompt,

    examples=examples,

    model_id="gpt-4o",  # Automatically selects OpenAI provider

    api_key=os.environ.get('OPENAI_API_KEY'),

    fence_output=True,

    use_schema_constraints=False

)

```



Note: OpenAI models require `fence_output=True` and `use_schema_constraints=False` because LangExtract doesn't implement schema constraints for OpenAI yet.



## Using Local LLMs with Ollama



LangExtract supports local inference using Ollama, allowing you to run models without API keys:



```python

import langextract as lx



result = lx.extract(

    text_or_documents=input_text,

    prompt_description=prompt,

    examples=examples,

    model_id="gemma2:2b",  # Automatically selects Ollama provider

    model_url="http://localhost:11434",

    fence_output=False,

    use_schema_constraints=False

)

```



**Quick setup:** Install Ollama from [ollama.com](https://ollama.com/), run `ollama pull gemma2:2b`, then `ollama serve`.



For detailed installation, Docker setup, and examples, see [`examples/ollama/`](examples/ollama/).



## More Examples



Additional examples of LangExtract in action:



### *Romeo and Juliet* Full Text Extraction



LangExtract can process complete documents directly from URLs. This example demonstrates extraction from the full text of *Romeo and Juliet* from Project Gutenberg (147,843 characters), showing parallel processing, sequential extraction passes, and performance optimization for long document processing.



**[View *Romeo and Juliet* Full Text Example →](https://github.com/google/langextract/blob/main/docs/examples/longer_text_example.md)**



### Medication Extraction



> **Disclaimer:** This demonstration is for illustrative purposes of LangExtract's baseline capability only. It does not represent a finished or approved product, is not intended to diagnose or suggest treatment of any disease or condition, and should not be used for medical advice.



LangExtract excels at extracting structured medical information from clinical text. These examples demonstrate both basic entity recognition (medication names, dosages, routes) and relationship extraction (connecting medications to their attributes), showing LangExtract's effectiveness for healthcare applications.



**[View Medication Examples →](https://github.com/google/langextract/blob/main/docs/examples/medication_examples.md)**



### Radiology Report Structuring: RadExtract



Explore RadExtract, a live interactive demo on HuggingFace Spaces that shows how LangExtract can automatically structure radiology reports. Try it directly in your browser with no setup required.



**[View RadExtract Demo →](https://huggingface.co/spaces/google/radextract)**



## Contributing



Contributions are welcome! See [CONTRIBUTING.md](https://github.com/google/langextract/blob/main/CONTRIBUTING.md) to get started

with development, testing, and pull requests. You must sign a

[Contributor License Agreement](https://cla.developers.google.com/about)

before submitting patches.



### Adding Custom Model Providers



LangExtract supports custom LLM providers through a plugin system. You can add support for new models by creating an external Python package that registers with LangExtract's provider registry. This allows you to:

- Add new model support without modifying the core library

- Distribute your provider independently

- Maintain custom dependencies



For detailed instructions, see the [Provider System Documentation](langextract/providers/README.md).



## Testing



To run tests locally from the source:



```bash

# Clone the repository

git clone https://github.com/google/langextract.git

cd langextract



# Install with test dependencies

pip install -e ".[test]"



# Run all tests

pytest tests

```



Or reproduce the full CI matrix locally with tox:



```bash

tox  # runs pylint + pytest on Python 3.10 and 3.11

```



### Ollama Integration Testing



If you have Ollama installed locally, you can run integration tests:



```bash

# Test Ollama integration (requires Ollama running with gemma2:2b model)

tox -e ollama-integration

```



This test will automatically detect if Ollama is available and run real inference tests.



## Development



### Code Formatting



This project uses automated formatting tools to maintain consistent code style:



```bash

# Auto-format all code

./autoformat.sh



# Or run formatters separately

isort langextract tests --profile google --line-length 80

pyink langextract tests --config pyproject.toml

```



### Pre-commit Hooks



For automatic formatting checks:

```bash

pre-commit install  # One-time setup

pre-commit run --all-files  # Manual run

```



### Linting



Run linting before submitting PRs:



```bash

pylint --rcfile=.pylintrc langextract tests

```



See [CONTRIBUTING.md](CONTRIBUTING.md) for full development guidelines.



## Disclaimer



This is not an officially supported Google product. If you use

LangExtract in production or publications, please cite accordingly and

acknowledge usage. Use is subject to the [Apache 2.0 License](https://github.com/google/langextract/blob/main/LICENSE).

For health-related applications, use of LangExtract is also subject to the

[Health AI Developer Foundations Terms of Use](https://developers.google.com/health-ai-developer-foundations/terms).



---



**Happy Extracting!**