Flit

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What Flit is

Flit is a free packaging and publishing tool for Python modules and packages intended for PyPI. It focuses on pure Python projects that do not need build steps, packaging one importable module or package at a time. Running flit init prompts for module information and creates a pyproject.toml file. Flit build then creates wheel and source distribution files, with either format available separately, while flit publish builds distributions and uploads them to PyPI, TestPyPI, or another configured package index. Subpackages and package data files are included automatically, and the package version is read from the module’s __version__ attribute. Flit uses pip for installation and requires Python 3, including Python 3’s pip to install it. It works on Linux and Windows. Dependencies are not managed automatically and must be entered in pyproject.toml. Flit cannot handle projects requiring build steps such as compiling C code or bundling JavaScript. Upload credentials can use keyring or environment variables, with password prompts when keyring is unavailable.

Who it suits

Flit suits Python developers publishing pure Python packages without build steps. It is less suitable when projects require compiled or other build processes, or automatic dependency management.

What it does well

Creates pyproject.toml through an interactive init command
Builds wheels and source distributions
Publishes to PyPI and other configured indexes
Includes subpackages and package data automatically
Supports reproducible wheel output from identical sources

What to know first

Cannot package projects requiring build steps
Dependencies must be added manually
Requires Python 3 and Python 3’s pip

Verdict

Flit provides a focused route from a simple Python package to build artifacts and PyPI publication. Its narrow scope keeps the workflow direct, but projects needing build steps or automatic dependency handling need another approach.

Facts from Flit's own pages

Automated publishing: Flit supports configuring upload servers and credentials through environment variables for automated releases, while warning that environment variables can expose passwords to other scripts and libraries in the environment. · flit.pypa.io, 9 Oct 2026
Build: The `flit build` command builds wheel and source distribution files. · flit.pypa.io, 8 Oct 2026
Builds: The `flit build` command builds a wheel and source distribution, with an option to build either format alone. · flit.pypa.io, 9 Oct 2026
Credential handling: Flit tries to store upload passwords securely using the keyring library; without keyring, it prompts for a password for each upload. · flit.pypa.io, 9 Oct 2026
Integrations: Flit uses pip for installation and supports uploading to PyPI, TestPyPI, or another configured package index. · flit.pypa.io, 9 Oct 2026
Intended use: Flit focuses on pure Python packages with no build steps, such as compiling C code or bundling JavaScript. · flit.pypa.io, 9 Oct 2026
Limit: build steps: Flit cannot be used for packages that require a build step. · flit.pypa.io, 8 Oct 2026
Limit: dependencies: Flit does not manage dependencies, which must be added to `pyproject.toml` by hand. · flit.pypa.io, 8 Oct 2026
Notable limitation: Flit cannot be used for packages that need a build step and does not manage dependencies automatically; dependencies must be added to `pyproject.toml` by hand. · flit.pypa.io, 9 Oct 2026
Package contents: Flit automatically includes subpackages and data files within a package. · flit.pypa.io, 8 Oct 2026
Packaging: Flit packages one importable module or package at a time and automatically includes its subpackages and package data files. · flit.pypa.io, 9 Oct 2026
Publishing: The `flit publish` command builds and uploads packages to PyPI or another configured package repository. · flit.pypa.io, 9 Oct 2026
Purpose: Flit is a simple way to put Python packages and modules on PyPI, aiming to reduce packaging effort and common mistakes. · flit.pypa.io, 9 Oct 2026
Python requirement: The Flit command line tool requires Python 3. · flit.pypa.io, 9 Oct 2026
Reproducible builds: Flit says wheels built from the same source code can be byte-for-byte identical, with file timestamps noted as a caveat that can be overridden using `SOURCE_DATE_EPOCH`. · flit.pypa.io, 9 Oct 2026
Setup: The `flit init` command helps set up package information in a `pyproject.toml` file. · flit.pypa.io, 9 Oct 2026
Target packages: Flit focuses on pure Python packages that have no build steps. · flit.pypa.io, 8 Oct 2026
Version metadata: Flit can obtain a package’s version from its `__version__` attribute. · flit.pypa.io, 9 Oct 2026
Windows support: The `--pth-file` install option works on Windows, where symlinks typically are not allowed. · flit.pypa.io, 8 Oct 2026

Where Flit stands on Freedom251

Python Package Managers#16 of 27