Principle:Langchain ai Langchain Package Configuration

Overview

A standard approach for configuring a Python package using pyproject.toml, including build system, dependencies, development groups, and tool settings.

Description

The Package Configuration principle describes how LangChain partner integration packages declare their build system, runtime dependencies, development dependency groups, and tool configurations through a single pyproject.toml file. This file is the central configuration point for each package in the monorepo.

Key configuration sections include:

• [build-system]: Specifies the build backend. LangChain packages use hatchling as the build backend, which provides fast, standards-compliant Python package building.
• [project]: Declares the package name, version, description, license, Python version constraints, classifiers, and runtime dependencies. The critical runtime dependency is langchain-core, which provides base abstractions.
• [project.urls]: Links to documentation, repository, issues, changelog, and community channels.
• [dependency-groups]: Defines separate dependency groups for different development activities:
  • test: Testing dependencies (pytest, pytest-asyncio, pytest-socket, langchain-tests)
  • test_integration: Additional dependencies needed only for integration tests
  • lint: Linting tools (ruff)
  • typing: Type-checking tools (mypy)
  • dev: General development dependencies
• [tool.uv.sources]: Maps internal LangChain packages to local editable installs for development, ensuring that changes to langchain-core or langchain-tests are immediately reflected.
• Tool configurations: Settings for mypy, ruff (linting and formatting), pytest, and coverage.

Usage

Apply this principle when:

• Creating a new pyproject.toml for a partner integration package.
• Adding or updating dependencies for an existing package.
• Configuring development tools (linter, formatter, type checker) for a package.
• Understanding how the monorepo's dependency resolution works across packages.

Theoretical Basis

Modern Python packaging relies on pyproject.toml as defined by PEP 517, PEP 518, and PEP 621. The dependency-groups pattern separates concerns so that CI can install only the tools needed for a specific job (e.g., uv sync --group test for testing, uv sync --group lint for linting).

[build-system]
requires = ["<build-backend>"]
build-backend = "<build-backend>.build"

[project]
name = "langchain-<integration>"
version = "<semver>"
dependencies = [
    "langchain-core>=<min>,<max>",
    # ... other runtime deps
]

[dependency-groups]
test = ["pytest", "langchain-tests", ...]
lint = ["ruff"]
typing = ["mypy"]

[tool.uv.sources]
langchain-core = { path = "../../core", editable = true }
langchain-tests = { path = "../../standard-tests", editable = true }

Related Pages

• Implementation:Langchain_ai_Langchain_Pyproject_Toml_Configuration