Python package guidelines - ArchWiki

# Python package guidelines

From ArchWiki

This document covers standards and guidelines on writing PKGBUILDs for Python software.

## Package naming

For Python 3 library modules, use `python-modulename`. Also use the prefix if the package provides a program that is strongly coupled to the Python ecosystem (e.g. pip or tox). For other applications, use only the program name.

The same applies to Python 2 except that the prefix (if needed) is `python2-`.

Note: The package name should be entirely lowercase.

## Architecture

See PKGBUILD#arch.

A Python package that contains C extensions using the `ext_modules` keyword in `setup.py`, is architecture-dependent. Otherwise it is most likely architecture-independent.

## Source

Download URLs linked from the PyPI website include an unpredictable hash that needs to be fetched from the PyPI website each time a package must be updated. This makes them unsuitable for use in a PKGBUILD. PyPI provides an alternative stable scheme: PKGBUILD#source `source=()` array should use the following URL templates:

Source package
  `https://files.pythonhosted.org/packages/source/${_name::1}/${_name}/${_name}-${pkgver}.tar.gz`
Bilingual wheel package (Python 2 and Python 3 compatible)
  `https://files.pythonhosted.org/packages/py2.py3/${_name::1}/$_name/$_name-$pkgver-py2.py3-none-any.whl`
Arch specific wheel package
  in this example for `source_x86_64=('...')`. Also `_py=py36` can be used to not repeat the python version:
  `https://files.pythonhosted.org/packages/$_py/${_name::1}/$_name/$_name-$pkgver-$_py-${_py}m-manylinux1_x86_64.whl`

Note that a custom `_name` variable is used instead of `pkgname` since python packages are generally prefixed with `python-`. This variable can generically be defined as follows:

    _name=${pkgname#python-}

## Installation methods

Python packages are generally installed using language-specific tools, such as pip or easy_install, which are comparable to dedicated package managers in that they are designed to fetch the source files from an online repository (usually PyPI, the Python Package Index) and track the relevant files (for a detailed comparison between the two, see pip vs easy_install).

However, for managing Python packages from within PKGBUILDs, the standard-provided distutils proves to be the most convenient solution since it uses the downloaded source package's `setup.py` and easily installs files under `$pkgdir/usr/lib/python<python version>/site-packages/$pkgname` directory.

### distutils

A distutils PKGBUILD is usually quite simple:

    build() {
        python setup.py build
    }

    package() {
        python setup.py install --root="$pkgdir/" --optimize=1 --skip-build
    }

where:

- python is replaced with the proper binary, `python` or `python2`
- `--root="$pkgdir/"` prevents trying to directly install in the host system instead of inside the package file, which would result in a permission error
- `--optimize=1` compiles optimized bytecode files (`.pyo` for Python 2, `opt-1.pyc` for Python 3) so they can be tracked by pacman.
- `--skip-build` optimizes away the unnecessary attempt to re-run the build steps already run in the `build()` function.

### setuptools

The Python packaging scene has largely migrated from distutils to setuptools, which is actively developed and functions as a drop-in replacement import in `setup.py`. The main difference for packagers is that setuptools is packaged separately from Python itself, and must be specified as a `makedepends`.

If the resulting package includes executables which import the `pkg_resources` module, then setuptools must be additionally specified as a `depends` in the split `package_*()` functions; alternatively, if the PKGBUILD only installs the Python package for a single version of Python, setuptools should be moved from `makedepends` to `depends`.

### pip

If you need to use pip (provided by python-pip and python2-pip), e.g. for installing wheel packages, remember to pass the following flags:

    PIP_CONFIG_FILE=/dev/null pip install --isolated --root="$pkgdir" --ignore-installed --no-deps *.whl

- `PIP_CONFIG_FILE=/dev/null` ignores `{/etc,~/.config}/pip.conf` that may be appending arbitrary flags to pip.
- `--isolated` ignores environment variables (and again `{/etc,~/.config}/pip/pip.conf`) that may otherwise also be appending arbitrary flags to pip.
- `--ignore-installed` is necessary until https://github.com/pypa/pip/issues/3063 is resolved (otherwise pip skips the install in the presence of an earlier `--user` install).
- `--no-deps` ensures, that dependencies do not get packaged together with the main package.

pip doesn't know how to generate `.pyo` files (see https://github.com/pypa/pip/issues/2209). In order to generate them manually after pip has installed the module, run:

    python -O -m compileall "${pkgdir}/path/to/module"

Warning: Use of pip and/or wheel packages is discouraged in favor of setuptools source packages, and should only be used when the latter is not a viable option (for example, packages which only come with wheel sources, and therefore cannot be installed using setuptools).

## Notes

Please do not install a directory named just `tests`, as it easily conflicts with other Python packages (for example, `/usr/lib/python2.7/site-packages/tests/`).

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