Flit

Flit is a lightweight way to put pure-Python packages and modules on PyPI with minimal configuration. Instead of hand-writing complex build scripts, you declare a small amount of metadata in pyproject.toml and let Flit build a wheel and sdist and upload them for you.

Maintained under the PyPA (Python Packaging Authority), Flit ships both a command-line tool (flit init/build/publish) for the common publishing workflow and flit_core, a PEP 517 build backend that other tools invoke to produce distributions. It deliberately targets simple projects, avoiding the overhead of general-purpose build systems.

What You Get

• A flit init command that scaffolds a pyproject.toml with project metadata and a chosen license
• Reproducible wheel and sdist builds from a single module or package
• One-command publishing to PyPI (flit publish)
• flit_core, a minimal PEP 517 build backend with almost no dependencies
• Version and metadata extraction directly from your module’s version and docstring

Common Use Cases

• Publishing small pure-Python libraries to PyPI with minimal boilerplate
• Serving as the PEP 517 build backend for a project via pyproject.toml
• Scaffolding a new package’s metadata and license with flit init
• Producing reproducible wheels and sdists in CI without a heavy build toolchain

Under The Hood

Architecture The repo is split into two packages. flit_core/flit_core/ is the dependency-light build backend: buildapi.py exposes the PEP 517 hooks, config.py parses pyproject.toml, and wheel.py/sdist.py assemble the distributions, with common.py handling metadata and version extraction. The user-facing flit/flit/ package layers the CLI on top: init.py scaffolds projects, build.py drives builds, upload.py publishes to PyPI, and a vcs/ module reads git/hg to decide which files to include. Keeping the backend separate lets build frontends depend on flit_core alone.

Tech Stack Pure Python targeting Python 3, using tomllib/tomli for configuration and requests for uploads, with the backend vendoring its few dependencies to stay lightweight. Packaging follows the PEP 517/518 standards it helped popularize, and testing runs through pytest and tox.

Code Quality As a PyPA project the codebase is mature and well-tested, with a tests/ suite, tox matrix, security policy, and a clean separation between the minimal backend and the richer CLI. License templates and SPDX data are bundled for the init workflow. Modules are small and single-purpose.

API Design The developer experience is Flit’s whole reason for existing: flit init then flit publish covers the common path, and adopting flit_core as a build backend is a three-line pyproject.toml block. Configuration is deliberately minimal, which keeps simple projects simple, at the cost of not handling compiled extensions or complex build steps.