setuptools-ext

This is a PEP 517 Build backend interface supporting fields in the Core metadata specifications which are otherwise difficult to provide using existing tools. Specifically, it allows declaring those fields marked with an "—" in the rightmost column of the table below by specifying them in a [tool.setuptools-ext] section of pyproject.toml. The backend otherwise functions identically to setuptools.build_meta, and is in fact a drop-in replacement for the default setuptools build backend.

Setuptools lacks a way to specify some fields, despite their validity in Python package metadata according to the spec. PEP 621 – Storing project metadata in pyproject.toml appears to have punted on some of the fields too.

Field	setup.py keyword	pyproject.toml name
Name	name	name
Version	version	version
Dynamic (multiple use)	—	dynamic
Platform (multiple use)	platforms	—
Supported-Platform (multiple use)	—	—
Summary	description	description
Description	long_description	readme
Description-Content-Type	long_description_content_type	readme
Keywords	keywords	keywords
Home-page	url	[project.urls]
Download-URL	download_url	—
Author	author	authors
Author-email	author_email	authors
Maintainer	maintainer	maintainers
Maintainer-email	maintainer_email	maintainers
License	license / license_files	license
Classifier (multiple use)	classifiers	classifiers
Requires-Dist (multiple use)	install_requires	dependencies
Requires-Python	python_requires	requires-python
Requires-External (multiple use)	—	—
Project-URL (multiple-use)	project_urls	[project.urls]
Provides-Extra (multiple use)	extras_require	[project.optional-dependencies]
Provides-Dist (multiple use)	—	—
Obsoletes-Dist (multiple use)	—	—

Reference links for the info above:

• Setuptools keywords and New and Changed setup() Keywords
• Declaring project metadata in pyproject.toml

Usage

To offer a simple example, if you want to add a Supported-Platform and the Requires-External field three times, producing these lines in the .dist-info/METADATA file:

Supported-Platform: RedHat 8.3
Requires-External: C
Requires-External: libpng (>=1.5)
Requires-External: make; sys_platform != "win32"

You would configure the tool like this in pyproject.toml, specifying a build dependency on setuptools-ext and then adding the fields in a [tool.setuptools-ext] section:

[build-system]
requires = ["setuptools-ext"]
build-backend = "setuptools_ext"

...

[tool.setuptools-ext]
supported-platform = [
    "RedHat 8.3",
]
requires-external = [
    "C",
    "libpng (>=1.5)",
    'make; sys_platform != "win32"'
]

The metadata fields may then be consumed by automated tooling for building RPM packages with system dependencies, for example.

Note: This package does not add new keyword arguments to setup.py (that's out of scope for a PEP 517 build backend).