pip show "License: UNKNOWN" despite license in Trove classifiers

[hugovk]

Environment

• pip version: pip 19.1.1 from /usr/local/lib/python3.7/site-packages/pip (python 3.7)
• Python version: 3.7
• OS: macOS Mojave 10.14.5

Description

License is UNKNOWN:

$ pip show pillow
Name: Pillow
Version: 6.1.0
Summary: Python Imaging Library (Fork)
Home-page: http://python-pillow.org
Author: Alex Clark (Fork Author)
Author-email: [email protected]
License: UNKNOWN
Location: /usr/local/lib/python3.7/site-packages/Pillow-6.1.0-py3.7-macosx-10.14-x86_64.egg
Requires:
Required-by:

Expected behavior

Pillow has no license= in setup() but has a known licence in the Trove classifiers:

        classifiers=[
...
            "License :: OSI Approved :: Historical Permission Notice and Disclaimer (HPND)",
...
        ],

These suggest license= shouldn't be used when there's a license in the Trove classifiers= (emphasis mine):

• https://packaging.python.org/specifications/core-metadata/?highlight=license#license

Text indicating the license covering the distribution where the license is not a selection from the “License” Trove classifiers. See “Classifier” below. This field may also be used to specify a particular version of a license which is named via the Classifier field, or to indicate a variation or exception to such a license.

• https://packaging.python.org/guides/distributing-packages-using-setuptools/?highlight=license#license

The license argument doesn’t have to indicate the license under which your package is being released, although you may optionally do so if you want. If you’re using a standard, well-known license, then your main indication can and should be via the classifiers argument. Classifiers exist for all major open-source licenses.

The “license” argument is more typically used to indicate differences from well-known licenses, or to include your own, unique license. As a general rule, it’s a good idea to use a standard, well-known license, both to avoid confusion and because some organizations avoid software whose license is unapproved.

The PR (pypa/packaging.python.org#492) for this latter said it's to "Indicate that this argument is meant for deviations from the Trove classifier, not instead of it."

Where does License from pip show come from?

Do we need to include license= to show the correct license in pip show, or is something extra needed in pip?

Thank you!

[xavfernandez]

pip show output could be improved to extract license from classifiers.
FWIW, in the meantime pip show -v can be used to output classifiers.

[cjerdonek]

I think it would probably be good to be able to tell from the output where the information is coming from, too. For example, there could be separate “License” and “License-classifiers” fields. And maybe “unknown” is suppressed if a classifier is present.

[hugovk]

The use case: a user runs pip show package to show the licence without having an additional step of visiting the repository to check the licence type for those that have to worry about such things (re: python-pillow/Pillow#3938).

In the short-term, we'll add license=, and suggest using pip show -v for other projects.

[pradyunsg]

Related discussion at: https://github.com/pypa/warehouse/issues/2996#issuecomment-425761711

I'm of the opinion that it'd be better to have someone spend the time and effort to fix the big fish here -- better specification of license metadata -- rather than add more bandages that need to be removed later.

[chrahunt]

Given the pending PEP mentioned in the linked issue, I would vote in favor of status quo (continuing to read from the license field). Hopefully with that initiative the metadata in general will improve over time, and we don't need to worry about backwards compatibility or supporting additional configuration like we would if implementing this issue.

[hugovk]

This is no longer a problem for Pillow, we've since added licence= to our metadata:

❯ pip show pillow
Name: pillow
Version: 11.0.0
Summary: Python Imaging Library (Fork)
Home-page: https://python-pillow.org
Author:
Author-email: "Jeffrey A. Clark" <[email protected]>
License: MIT-CMU
Location: /Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages
Requires:
Required-by: matplotlib, pillow_heif

I'm of the opinion that it'd be better to have someone spend the time and effort to fix the big fish here -- better specification of license metadata -- rather than add more bandages that need to be removed later.

The bigger fish are being dealt with in PEP 639 – Improving License Clarity with Better Package Metadata, provisionally accepted and being implemented across the packaging ecosystem.

I think we can close this now.