What? # PEP 639 defines a spec on how to document licences used in Python projects. Instead of using a Trove classifier such as “License :: OSI Approved :: BSD License”, which is imprecise (for example, which BSD licence?), the SPDX licence expression syntax is used. How? # pyproject.toml# Change pyproject.toml as follows. I usually use Hatchling as a build backend, and support was added in 1.27: [build-system] build-backend = "hatchling.build" requires = [ "hatch-vcs", - "hatchling", + "...