Bootstrapping

Flit is itself packaged using Flit, as are some foundational packaging tools such as pep517. So where can you start if you need to install everything from source?

Note

For most users, pip handles all this automatically. You should only need to deal with this if you’re building things entirely from scratch, such as putting Python packages into another package format.

The key piece is flit_core. This is a package which can build itself using nothing except Python and the standard library. From an unpacked source archive, you can make a wheel by running:

python -m flit_core.wheel

And then you can install this wheel with the bootstrap_install.py script included in the sdist (or by unzipping it to the correct directory):

# Install to site-packages for this Python:
python bootstrap_install.py dist/flit_core-*.whl

# Install somewhere else:
python bootstrap_install.py --installdir /path/to/site-packages dist/flit_core-*.whl

Note

This note only applies if you need to unbundle or unvendor dependencies.

flit_core unconditionally bundles the tomli TOML parser, to avoid a dependency cycle for older versions of Python that don’t include the standard library tomllib module.

The tomli library is only used on Python 3.10 and older, meaning that if you use Python 3.11 or newer you can simply remove the bundled tomli. Otherwise, you must special-case installing flit_core and/or tomli to resolve the dependency cycle between the two packages.

After flit_core, I recommend that you get installer set up. You can use python -m flit_core.wheel again to make a wheel, and then use installer itself (from the source directory) to install it.

After that, you probably want to get build and its dependencies installed as the goal of the bootstrapping phase. You can then use build to create wheels of any other Python packages, and installer to install them.