fromager

Fromager is a tool for rebuilding complete dependency trees of Python wheels from source.

Goals

Fromager is designed to guarantee that:

• Every binary package you install was built from source in a reproducible environment compatible with your own.

• All dependencies are also built from source, no prebuilt binaries.

• The build tools themselves are built from source, ensuring a fully transparent toolchain.

• Builds can be customized for your needs: applying patches, adjusting compiler options, or producing build variants.

Design Principles

Fromager automates the build process with sensible defaults that work for most PEP-517–compatible packages. At the same time, every step can be overridden for special cases, without baking those exceptions into Fromager itself.

Build Collections of Wheels

Fromager can also build wheels in collections, rather than individually. Managing dependencies as a unified group ensures that:

• Packages built against one another remain ABI-compatible.

• All versions are resolved consistently, so the resulting wheels can be installed together without conflicts.

This approach makes Fromager especially useful in Python-heavy domains like AI, where reproducibility and compatibility across complex dependency trees are essential.

Using private registries

Fromager uses the requests library and pip at different points for talking to package registries. Both support authenticating to remote servers in various ways. The simplest way to integrate the authentication with fromager is to have a netrc file with a valid entry for the host. The file will be read from ~/.netrc by default. Another location can be specified by setting the NETRC environment variable.

For example, to use a gitlab package registry, use a personal access token as documented in this issue:

machine gitlab.com login oauth2 password $token

Determining versions via GitHub tags

In some cases, the builder might have to use tags on GitHub to determine the version of a project instead of looking at pypi.org. To avoid rate limit or to access private GitHub repository, a personal access token can be passed to fromager by setting the following environment variable:

GITHUB_TOKEN=<access_token>

Additional docs

• Using fromager
• Package build customization instructions
• Developer instructions

What's with the name?

Python's name comes from Monty Python, the group of comedians. One of their skits is about a cheese shop that has no cheese in stock. The original Python Package Index (pypi.org) was called The Cheeseshop, in part because it hosted metadata about packages but no actual packages. The wheel file format was selected because cheese is packaged in wheels. And "fromager" is the French word for someone who makes or sells cheese.