[Docs] Clarify usage of include_package_data/package_data/exclude_package_data on package data files

[DanielYang59]

Summary of changes

• Clarify usage of include_package_data/package_data/exclude_package_data in pyproject.toml on inclusion of package data files, as a follow up of [BUG] Selection of package data in sdist and wheels with include-package-data keyword #4638
• Clarify priority level [BUG] Selection of package data in sdist and wheels with include-package-data keyword #4638 (comment)

[DanielYang59]

The include_package_data keyword would only have an effect when condition is met, perhaps it's good to state these upfront?

[abravalheri]

Thank you very much for your contribution!

[abravalheri]

Thank you for your suggestion. I understand that your main objective was to clarify what “data files” are.

While this intention is very appreciated and welcome, the proposed parenthesis seem to suggest: data file = file not included in the "default set". This could lead to confusion, as what defines a data file is not fundamentally related to whether a file is included in the default set or not. For example, we could change setuptools to start including .json files automatically, but that would not make them more or less “data file”-y.

Could you please have a look at the following suggestion (which adds a new paragraph before the original text)? Would this address your concerns?

Suggested change

	Old packaging installation methods in the Python ecosystem have
	traditionally allowed the inclusion of "data files" (files beyond
	:ref:`the default set <manifest>` ), which are placed in a platform-specific
	location. However, the most common use case for data files distributed
	with a package is for use *by* the package, usually by including the
	data files **inside the package directory**.
	``Setuptools`` focuses on this most common type of data files and offers three ways
	In the Python ecosystem, the term "data files" is used in various complex scenarios
	and can have nuanced meanings.
	For the purposes of this documentation, we define "data files" as non-Python files
	that are installed alongside Python modules and packages on the user's machine
	when they install a :term:`distribution <Distribution Package>` from PyPI
	or via a ``.whl`` file.
	These files are typically intended for use at runtime by the package itself or
	to influence the behavior of other packages or systems.
	They may also be referred to as "resource files."
	Old packaging installation methods in the Python ecosystem
	have traditionally allowed installation of "data files", which
	are placed in a platform-specific location. However, the most common use case
	for data files distributed with a package is for use *by* the package, usually
	by including the data files **inside the package directory**.
	Setuptools focuses on this most common type of data files and offers three ways

Does this look good to you?

[DanielYang59]

Thank you for your suggestion. I understand that your main objective was to clarify what “data files” are.

Yes exactly. Because this is the starting sentence of the Data Files Support section, and we have to make sure users understand what is considered "data file" in the first place, such that they could decide whether they even need these keywords at all.

For example C source code/READMEs are not "Python" files, but we don't need to declare them to include them into the package. And therefore we might need to clarify the following definition of "data files":

we define "data files" as non-Python files

the proposed parenthesis seem to suggest: data file = file not included in the "default set". This could lead to confusion, as what defines a data file is not fundamentally related to whether a file is included in the default set or not.

Thanks a ton for the clarification! Yes my sketch indeed would need more discussion and check.

They may also be referred to as "resource files."

Personally I think the following terminologies are already very confusing: "package data", "data file", "source distribution", "files inside the wheel", and their difference is pretty unclear, and can we somehow define/clarify them, and perhaps avoid introducing more synonyms ("resource files" in this case)?

[abravalheri]

I have no problems with omitting resource files, I just mentioned before because other packages started calling them that way (e.g. importlib_resources). Please feel free to use and modify my suggestion to align with your vision in the contribution.

---

For example C source code/READMEs are not "Python" files, but we don't need to declare them to include them into the package.

Yes, in this case C/README files are not data files, because they don't fit in the remaining part of the suggested definition:

... that are installed alongside Python modules and packages on the user's machine
when they install a :term:`distribution <Distribution Package>` from PyPI
or via a ``.whl`` file.
These files are typically intended for use at runtime by the package itself or
to influence the behavior of other packages or systems.

C-files are not installed along side Python files in the user's machine and also are not intended to be used in runtime, right?

---

I just noticed this from official Python docs:

MANIFEST.in does not affect binary distributions such as wheels.

That is not 100% precise is it? MANIFEST.in determines what goes into the sdist, and then the contents of the sdist influence what goes into the wheel (specially when include-package-data = true which is the default)... So there is a potential indirect effect there. That is because the build process works more or less like in the mermaidjs diagram below¹:

graph LR
    src[fa:fa-laptop-code source code] --> b1(fa:fa-hammer)
    
    subgraph build process
      b1 --> sdist(fa:fa-file-code sdist) --> b2(fa:fa-hammer)
      b2 --> wheel(fa:fa-box wheel)
       
      build([build dependencies]) --> b1
      build([build dependencies]) --> b2
    end

    subgraph installation process
        wheel --> pkg
        pkg(fa:fa-box-open) --> inst[fa:fa-python installed packages]
        runtime([runtime dependencies]) --> inst
    end

    classDef deps fill:#2aa198,stroke:#333
    classDef env fill:#6c71c4,stroke:#333
    build:::deps
    runtime:::deps

Loading

Footnotes

1. The "build process" creates distribution artifacts/packages. sdist distributions are meant to be platform independent (but may contain varying levels of optimisation - e.g. compiling Python to C via Cython). wheel distributions contain the final files meant to be directly copied to the user's machine, and therefore may be platform specific. ↩

[DanielYang59]

I just noticed this from official Python docs:

MANIFEST.in does not affect binary distributions such as wheels.

[DanielYang59]

I would tag and explain something I want to change (I find myself lose track of what I was originally intended if I overthink), please free feel to comment.

I believe the source (PyPI vs file) is not important here, but whether we're installing from a binary distribution (.whl) or source distribution that matters.

[abravalheri]

We are probably better off if we don't define data files in terms of source distributions or source trees... Because then we enter in muddy waters (as source distributions and source tree may have any kinds of files).

[DanielYang59]

We are probably better off if we don't define data files in terms of source distributions or source trees

Sorry it looks like I might have caused confusion here. I was suggesting:

- When they install a distribution from PyPI or via a `.whl` file
+ When they install a distribution from source distribution or via a `.whl` file

Because install from PyPI is not important here, because by install from PyPI, we could install both from .whl file (if wheel is built for that particular platform) or source distribution. I hope I didn't misunderstand anything?

[DanielYang59]

@abravalheri I believe I have included everything I want to include, perhaps it's time to polish the language and check the correctness and finalize this PR?

Some questions unrelated to this PR:

1. The following file name has spaces in it, is it intended or maybe rename it to a proper Unix name (escaping spaces looks quite messy)?: https://github.com/pypa/setuptools/blob/main/docs/python%202%20sunset.rst
2. I got the following notifications while building docs locally, perhaps update conf.py accordingly?

intersphinx inventory has moved: https://twine.readthedocs.io/en/stable//objects.inv -> https://twine.readthedocs.io/en/stable/objects.inv
inventory <https://build.pypa.io/en/latest> contains multiple definitions for std:label:python--m-build--v
intersphinx inventory has moved: https://packaging.python.org/en/latest//objects.inv -> https://packaging.python.org/en/latest/objects.inv
intersphinx inventory has moved: https://packaging.pypa.io/en/latest//objects.inv -> https://packaging.pypa.io/en/latest/objects.inv