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Lance Graph

A high-performance Cypher-capable graph query engine with Python bindings for building scalable, serverless knowledge graphs.

Lance Graph combines a Rust-powered Cypher query engine with Python APIs for:

  • Fast graph queries using Cypher query language
  • AI-powered knowledge extraction from text (via LLM)
  • Lance-backed storage for efficient graph data management
  • Natural language Q&A over your knowledge graphs
  • FastAPI web service for graph queries

Installation

pip install lance-graph

Quick Start

1. Simple Cypher Query

import pyarrow as pa
from lance_graph import CypherQuery, GraphConfig

cfg = (
    GraphConfig.builder()
    .with_node_label("Person", "id")
    .with_node_label("City", "id")
    .with_relationship("lives_in", "src", "dst")
    .build()
)

datasets = {
    "Person": pa.table({"id": [1, 2], "name": ["Alice", "Bob"]}),
    "City": pa.table({"id": [10, 20], "name": ["London", "Sydney"]}),
    "lives_in": pa.table({"src": [1, 2], "dst": [10, 20]}),
}

query = """
    MATCH (p:Person)-[:lives_in]->(c:City)
    RETURN p.name, c.name
"""

result = CypherQuery(query).with_config(cfg).execute(datasets)
print(result.to_pylist())

[{'p.name': 'Alice', 'c.name': 'London'}, {'p.name': 'Bob', 'c.name': 'Sydney'}]

2. Build a Knowledge Graph from Text

from pathlib import Path
from knowledge_graph import (
    KnowledgeGraphConfig,
    LanceKnowledgeGraph,
    LanceGraphStore,
    get_extractor,
)
from knowledge_graph.cli.ingest import extract_and_add

# Initialize knowledge graph
config = KnowledgeGraphConfig.from_root(Path("./my_graph"))
config.ensure_directories()

# Create schema
schema_path = config.resolved_schema_path()
if not schema_path.exists():
    schema_content = """
nodes:
  Entity:
    id_field: entity_id

relationships:
  RELATIONSHIP:
    source: source_entity_id
    target: target_entity_id
"""
    schema_path.write_text(schema_content, encoding="utf-8")

store = LanceGraphStore(config)
store.ensure_layout()

graph_config = config.load_graph_config()
kg = LanceKnowledgeGraph(graph_config, storage=store)
kg.ensure_initialized()

# Extract and add entities/relationships from text
# Using heuristic extractor for testing without API key
extractor = get_extractor("heuristic")
# or using LLM extractor (requires API key)
# extractor = get_extractor("llm", llm_model="gpt-4o-mini")
text = """
Albert Einstein developed the theory of relativity at Princeton.
Marie Curie discovered radioactivity in Paris.
"""

extract_and_add(text, kg, extractor, embedding_generator=None)

# Query the graph
result = kg.query("""
    MATCH (e:Entity)
    RETURN e.name, e.entity_type
    LIMIT 10
""")
print(result.to_pylist())

3. Natural Language Q&A

from knowledge_graph.llm.qa import ask_question

# Ask questions in natural language
answer = ask_question(
    "Who discovered radioactivity?",
    kg,
    llm_model="gpt-4o-mini"
)
print(answer)
# Output: Marie Curie discovered radioactivity.

Command-Line Interface

Lance Graph includes a CLI for building and querying knowledge graphs:

# Initialize and extract
knowledge_graph --root ./my_graph --init
knowledge_graph --root ./my_graph --extract-and-add notes.txt

# Query with Cypher
knowledge_graph --root ./my_graph "MATCH (e:Entity) RETURN e.name LIMIT 10"

# Natural language Q&A
knowledge_graph --root ./my_graph --ask "Who discovered DNA?"

For complete CLI documentation and examples, see the main README.

Requirements

  • Python 3.11+
  • Optional: OpenAI API key for LLM extraction

Contributing

Lance Graph is open source! Contributions are welcome.

Quick start

cd python
uv venv --python 3.11 .venv
source .venv/bin/activate
uv pip install maturin[patchelf]
uv pip install -e '.[tests]'
maturin develop
pytest python/tests/ -v

Development workflow

For linting and type checks:

# Install dev dependencies
uv pip install -e '.[dev]'

# Run linters and type checker
ruff format python/              # format code
ruff check python/               # lint code
pyright                          # type check

# Run specific tests
pytest python/tests/test_graph.py::test_basic_node_selection -v

# Rebuild extension after Rust changes
maturin develop

If another virtual environment is already active, run deactivate (or unset VIRTUAL_ENV) before invoking uv run so uv binds to .venv.

Repository layout

  • python/src/ – PyO3 bridge that exposes graph APIs to Python
  • python/python/lance_graph/ – pure-Python wrapper and __init__
  • python/python/knowledge_graph/ – CLI, FastAPI, and extractor utilities built on Lance
  • python/python/tests/ – graph-centric functional tests

For more information on development setup, building from source, running tests, and code quality guidelines, see DEVELOPMENT.md.

License

Apache 2.0

Links