distutils-r1 — standard Python build systems

The distutils-r1 eclass is used to facilitate build systems using setup.py (distutils and its derivatives, notably setuptools) or pyproject.toml (flit, poetry). It is built on top of python-r1 and python-single-r1, and therefore supports efficiently building multi-impl and single-impl packages.

Eclass reference: distutils-r1.eclass(5)

The PEP 517 and legacy modes

The distutils-r1 eclass has currently two modes of operation: the PEP 517 mode and the legacy mode. The former mode should be preferred for new ebuilds; the latter is provided for backwards compatibility and packages that are incompatible with the other mode.

The PEP 517 mode uses backends as defined by PEP 517 to build packages. It supports a greater number of Python build systems at the cost of flexibility and performance. In the eclass implementation, the PEP 517 backend is used to build a wheel (i.e. a zip archive) with the package and then an installer tool is used to install the wheel into a staging directory. The complete process is done in compile phase, and the install phase merely moves the files into the image directory.

The PEP 517 mode also features a ‘no build system’ mode for packages that do not or cannot use a PEP 517-compliant build backend.

The legacy mode invokes the setup.py script directly. The build command is invoked to populate the build directory in the compile phase, then the install command is used in the install phase. Normally, this mode works only for packages using backwards-compatible distutils derivatives. Additionally, it supports flit and poetry through pyproject2setuppy hack. This mode relies on deprecated features.

The PEP 517 mode is enabled via declaring the DISTUTILS_USE_PEP517 variable. The legal values can be found in the PEP 517 build systems section. If unset, the legacy mode is used.

Basic use (PEP 517 mode)

By default, distutils-r1 sets appropriate metadata variables and exports a full set of phase functions necessary to install packages using Python build systems.

The DISTUTILS_USE_PEP517 variable is used to enable the modern PEP 517 mode and declare the build system used. The eclass automatically generates a build-time dependency on the packages needed for the build system.

The simplest case of ebuild is:

 # Copyright 1999-2022 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2


 PYTHON_COMPAT=( python3_{8..10} pypy3 )
 inherit distutils-r1

 DESCRIPTION="Makes working with XML feel like you are working with JSON"
 HOMEPAGE="https://github.com/martinblech/xmltodict/ https://pypi.org/project/xmltodict/"

 KEYWORDS="~amd64 ~arm ~arm64 ~x86"

Source archives

The vast majority of Python packages can be found in the Python Package Index (PyPI). Often this includes both source (sdist) and binary (wheel) packages. In addition to that, many packages have public VCS repositories with an automatic archive generation mechanism (e.g. GitHub).

The current recommendation is to prefer source distributions from PyPI if and only if they include all files needed for the package, especially tests. If the PyPI distribution is missing some files, VCS generated archives should be used instead. In some extreme cases, it may be necessary to use both and combine the files contained in them (e.g. to combine files pregenerated using NodeJS from sdist with tests from GitHub archive).

When fetching archives from PyPI, pypi.eclass should be used. It is documented in its own chapter: pypi — helper eclass for PyPI archives.

When using generated archives, it is recommended to append a unique suffix (in case of GitHub, using a .gh.tar.gz suffix is requested) to the distfile name, in order to make the archive clearly distinguishable from the upstream provided tarball and to use a filename that matches the top directory inside the archive, e.g.:

        -> ${P}.gh.tar.gz

Note that unlike sdist archives, snapshots are often missing generated files. This has some implications, notably:

  1. If the package uses setuptools_scm or a similar package, the version string may need to be provided explicitly, cf. setuptools_scm (flit_scm, hatch-vcs, pdm-backend) and snapshots.

  2. If the package uses Cython, the C files need to be generated and an explicit BDEPEND on dev-python/cython needs to be added. However, regenerating them is recommended anyway, cf. packages using Cython.


Dependencies on Python packages are declared using the same method as the underlying eclass — that is, python-r1 or python-single-r1.

In packages using dev-python/setuptools, dependencies are often specified in setup.py or setup.cfg file. The install_requires key specifies runtime dependencies, setup_requires pure build-time dependencies, extras_require optional dependencies. Test dependencies are sometimes specified as one of the ‘extras’, and sometimes as tests_require.

Setuptools strictly enforces setup_requires at build time, and tests_require when running setup.py test. Runtime dependencies are enforced only when starting installed programs via entry points.

In other cases, dependencies are listed in additional files named e.g. requirements.txt. They could be also found in test runner setup (tox.ini) or CI setup files (.travis.yml). Finally, you can grep source code for import statements.

In general, you should take special care when listing dependencies of Python packages. Upstreams sometimes specify indirect dependencies, often list packages that are not strictly relevant to Gentoo runs but used on CI/CD setup, unnecessarily restrict version requirements.

Most of the time, runtime dependencies do not need to be present at build time. However, they do need to be copied there if the Python modules needing them are imported at build time. Often this is the case when running tests, hence the following logic is common in Python ebuilds:

BDEPEND="test? ( ${RDEPEND} )"

There are two different approaches used for optional runtime dependencies. Some packages are installing them conditionally to USE flags (this is generally acceptable as long as package builds quickly), others list them in pkg_postinst() messages. It is recommended that optional test dependencies are used unconditionally (to ensure the widest test coverage, and avoid unpredictable test failures on users who have more dependencies installed).

python-single-r1 variant

Normally, distutils-r1 uses python-r1 to build multi-impl packages, and this is the recommended mode. However, in some cases you will need to use python-single-r1 instead, especially if you need to depend on other packages using that eclass.

The single-impl mode can be enabled by setting DISTUTILS_SINGLE_IMPL variable before inheriting the eclass. The eclass aims to provide maximum compatibility between these two modes, so most of the existing code will work with either. However, the functions specific to the underlying eclass are not compatible — e.g. the dependencies need to be rewritten.

 # Copyright 1999-2022 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2


 PYTHON_COMPAT=( python3_{8..10} )

 inherit distutils-r1

 DESCRIPTION="Pythonic layer on top of the ROOT framework's PyROOT bindings"

 KEYWORDS="~amd64 ~x86 ~amd64-linux ~x86-linux"

     $(python_gen_cond_dep '


PEP 517 build systems

The majority of examples in this guide assume using setuptools build system. However, PEP 517 mode provides support for other build systems.

In order to determine the correct build system used, read the pyproject.toml file. An example file could start with:

requires = ["flit_core >=3.6.0,<4"]
build-backend = "flit_core.buildapi"

The requires key indicates the packages required in order to run the build system, while build-backend indicates the module (and optionally the class) providing the build system backend. The eclass maintains a mapping of backend paths to the respective DISTUTILS_USE_PEP517 and automatically suggests the correct value.

The following table summarizes supported backends.

USE_PEP517 value

Provider package






















(none, see below)


















setuptools.build_meta setuptools.__legacy__.build_meta






(various, see below)

The eclass recognizes two special values: no and standalone. no is used to enable ‘no build system’ mode as described in installing packages without a PEP 517 build backend. standalone indicates that the package itself provides its own build backend.

Legacy packages that provide setup.py but no pyproject.toml (or do not define a backend inside it) should be installed via the setuptools backend (this applies to pure distutils packages as well). The eclass automatically uses the legacy setuptools backend for them.

setuptools_scm (flit_scm, hatch-vcs, pdm-backend) and snapshots

setuptools_scm is a package providing additional features for running inside a VCS checkout, in particular the ability to determine version from VCS tags. However, this may not work when building from a GitHub snapshot:

Traceback (most recent call last):
  File "/tmp/executing-0.5.2/setup.py", line 4, in <module>
  File "/usr/lib/python3.9/site-packages/setuptools/__init__.py", line 143, in setup
  File "/usr/lib/python3.9/site-packages/setuptools/__init__.py", line 131, in _install_setup_requires
    dist = distutils.core.Distribution(dict(
  File "/usr/lib/python3.9/site-packages/setuptools/dist.py", line 425, in __init__
    _Distribution.__init__(self, {
  File "/usr/lib/python3.9/distutils/dist.py", line 292, in __init__
  File "/usr/lib/python3.9/site-packages/setuptools/dist.py", line 717, in finalize_options
  File "/usr/lib/python3.9/site-packages/setuptools_scm/integration.py", line 48, in infer_version
    dist.metadata.version = _get_version(config)
  File "/usr/lib/python3.9/site-packages/setuptools_scm/__init__.py", line 148, in _get_version
    parsed_version = _do_parse(config)
  File "/usr/lib/python3.9/site-packages/setuptools_scm/__init__.py", line 110, in _do_parse
    raise LookupError(
LookupError: setuptools-scm was unable to detect version for '/tmp/executing-0.5.2'.

Make sure you're either building from a fully intact git repository or PyPI tarballs. Most other sources (such as GitHub's tarballs, a git checkout without the .git folder) don't contain the necessary metadata and will not work.

For example, if you're using pip, instead of https://github.com/user/proj/archive/master.zip use git+https://github.com/user/proj.git#egg=proj

This problem can be resolved by providing the correct version externally via SETUPTOOLS_SCM_PRETEND_VERSION:


The flit_scm and hatch-vcs packages are both built on top of setuptools_scm. The same approach applies to both of them.


While SETUPTOOLS_SCM_PRETEND_VERSION is sufficient to make the package build, setuptools may install incomplete set of package data files. Please take special care to verify that all files are installed.

The pdm-backend package reinvents its own SCM version support, and unlike setuptools_scm, it uses 0.0.0 rather than throwing an error when the version cannot be determined. The override for this backend can be set using a similarly purposed environment variable:


Packages installing extensions (C, Rust…)

Python extensions are compiled (C, Cython, Rust…) loadable modules. They can generally be recognized by the presence of .so files in site-packages directory.

The eclass provides a DISTUTILS_EXT control variable to enable additional features related to extensions. These are:

  • DEPEND class dependency on the Python implementation — needed for cross-compilation (unless DISTUTILS_OPTIONAL is used, then the DEPEND needs to be added manually).

  • IUSE=debug flag that is used to control whether the extensions are compiled with assertions enabled (among others, used to verify whether the Python API is used correctly).

  • calling esetup.py build_ext to compile C files using parallel jobs.

The variable needs to be set prior to inheriting the eclass, e.g.:

 # Copyright 2023 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2


 PYTHON_COMPAT=( python3_{10..11} pypy3 )

 inherit distutils-r1

Note that it should be enabled even if the extensions are only built conditionally to USE flags. Most of the additions need to be done in global scope anyway, and making the DEPEND conditional isn’t considered worth the added complexity.

In general, you don’t need to worry about adding the variable. The eclass should automatically print a QA warning if DISTUTILS_EXT is missing:

* Python extension modules (*.so) found installed. Please set:
* in the ebuild.

Packages using Cython

Cython is a static compiler that permits writing Python extensions in a hybrid of C and Python. Cython files are compiled into C code that is compatible with multiple Python interpreters. This makes it possible for packages to include pregenerated C files and build the respective extensions without exposing the Cython dependency.

In Gentoo, it is always recommended to depend on dev-python/cython and regenerate the C files. This guarantees that bug fixes found in newer versions of Cython are taken advantage of. Using shipped files could e.g. cause compatibility issues with newer versions of Python.

Depending on the package in question, forcing regeneration could be as simple as removing the pregenerated files:


src_configure() {
    rm src/frobnicate.c || die

However, in some cases packages utilize the generated C files directly in setup.py. In these cases, sometimes a Makefile is provided to run Cythonize. It is also possible to call Cython directly:


src_configure() {
    cython -3 jq.pyx -o jq.c || die

Note that Cython needs to be called only once, as the resulting code is compatible with all Python versions.

Parallel build race conditions

The distutils build system has a major unresolved bug regarding race conditions. If the same source file is used to build multiple Python extensions, the build can start multiple simultaneous compiler processes using the same output file. As a result, there is a race between the compilers writing output file and link editors reading it. This generally does not cause immediate build failures but results in broken extensions causing cryptic issues in reverse dependencies.

For example, a miscompilation of dev-python/pandas have recently caused breakage in dev-python/dask:

/usr/lib/python3.8/site-packages/pandas/__init__.py:29: in <module>
    from pandas._libs import hashtable as _hashtable, lib as _lib, tslib as _tslib
/usr/lib/python3.8/site-packages/pandas/_libs/__init__.py:13: in <module>
    from pandas._libs.interval import Interval
pandas/_libs/interval.pyx:1: in init pandas._libs.interval
pandas/_libs/hashtable.pyx:1: in init pandas._libs.hashtable
pandas/_libs/missing.pyx:1: in init pandas._libs.missing
/usr/lib/python3.8/site-packages/pandas/_libs/tslibs/__init__.py:30: in <module>
    from .conversion import OutOfBoundsTimedelta, localize_pydatetime
E   ImportError: /usr/lib/python3.8/site-packages/pandas/_libs/tslibs/conversion.cpython-38-x86_64-linux-gnu.so: undefined symbol: pandas_datetime_to_datetimestruct

The easiest way to workaround the problem in ebuild is to append -j1 in python_compile sub-phase.

The common way of working around the problem upstream is to create additional .c files that #include the original file, and use unique source files for every extension.

Sub-phase functions

Ebuilds define phase functions in order to conveniently override parts of the build process. distutils-r1 extends this concept by introducing sub-phases. All src_* phases in ebuild are split into two sub-phases: python_* sub-phases that are run in a loop for all enabled interpreters, and python_*_all sub-phases that comprise the common code to be run only once.

Sub-phase functions behave similarly to phase functions. They are run if defined by the ebuild. If they’re not, the default implementation is run (if any). The ebuild overrides can call the default as distutils-r1_<sub-phase>, the same way it can call eclass’ phase function defaults.

There are 10 sub-phases corresponding to 5 phase functions. They are run in the following order:

  1. python_prepare_all (for src_prepare, has default)

  2. python_prepare (for each impl.)

  3. python_configure (for src_configure, for each impl.)

  4. python_configure_all

  5. python_compile (for src_compile, for each impl., has default)

  6. python_compile_all

  7. python_test (for src_test, for each impl.)

  8. python_test_all

  9. python_install (for src_install, for each impl., has default)

  10. python_install_all (has default)

Note that normally all phases are run in the source directory, while defining ${BUILD_DIR} to a dedicated build directory for each implementation. However, if in-source builds are enabled, all phases are run in these build directories.


python_prepare_all is responsible for applying changes to the package sources that are common to all Python implementations. The default implementation performs the tasks of default_src_prepare (applying patches), as well as eclass-specific tasks: removing ez_setup (method of bootstrapping setuptools used in old packages) and handling pyproject.toml. In the end, the function copies sources to build dirs if in-source build is requested.

If additional changes need to be done to the package, either this sub-phase or src_prepare in general can be replaced. However, you should always call the original implementation from your override. For example, you could use it to strip extraneous dependencies or broken tests:

python_prepare_all() {
    # FIXME
    rm tests/test_pytest_plugin.py || die
    sed -i -e 's:test_testcase_no_app:_&:' tests/test_test_utils.py || die

    # remove pointless dep on pytest-cov
    sed -i -e '/addopts/s/--cov=aiohttp//' pytest.ini || die


python_prepare is responsible for applying changes specific to one interpreter. It has no default implementation. When defined, in-source builds are enabled implicitly as sources need to be duplicated to apply implementation-specific changes.

In the following example, it is used to remove a CLI script whose dependencies only support Python 3.8 and 3.9 at the moment. Naturally, since this modification needs to be done on a subset of all Python interpreters, the eclass needs to keep a separate copy of the sources for every one of them. This is why python_prepare automatically enables in-source builds.

python_prepare() {
    if ! use cli || ! has "${EPYTHON}" python3.{7..9}; then
        sed -i -e '/console_scripts/d' setup.py || die


python_configure and python_configure_all have no default functionality. The former is convenient for running additional configuration steps if needed by the package, the latter for defining global environment variables.

python_configure() {
    esetup.py configure $(usex mpi --mpi '')
python_configure_all() {


python_compile normally builds the package. It is sometimes used to pass additional arguments to the build step. For example, it can be used to disable parallel extension builds in packages that are broken with it:

python_compile() {
    distutils-r1_python_compile -j1

python_compile_all has no default implementation. It is convenient for performing additional common build steps, in particular for building the documentation (see distutils_enable_sphinx).

python_compile_all() {
    use doc && emake -C docs html


python_test is responsible for running tests. It has no default implementation but you are strongly encouraged to provide one (either directly or via distutils_enable_tests). python_test_all can be used to run additional testing code that is not specific to Python.

python_test() {
    "${EPYTHON}" TestBitVector/Test.py || die "Tests fail with ${EPYTHON}"


python_install installs the package’s Python part. It is usually redefined in order to pass additional setup.py arguments or to install additional Python modules.

python_install() {

    # ensure data files for tests are getting installed too
    python_moduleinto collada/tests/
    python_domodule collada/tests/data

python_install_all installs documentation via einstalldocs. It is usually defined by ebuilds to install additional common files such as bash completions or examples.

python_install_all() {
    if use examples; then
        docinto examples
        dodoc -r Sample_Code/.
        docompress -x /usr/share/doc/${PF}/examples

Passing arguments to setup.py

There are two main methods of accepting additional command-line options in setup.py scripts: using global options and via command options.

Global options are usually implemented through manipulating sys.path directly. The recommended way to use them is to specify them via DISTUTILS_ARGS array:

src_configure() {
    DISTUTILS_ARGS=( --external )

The options specified via DISTUTILS_ARGS are passed to all esetup.py invocations, as well as to the setuptools PEP 517 backend (using the --global-option setting). For future compatibility, it is recommended to avoid adding command names to DISTUTILS_ARGS.

The recommended way to pass command options is to use the setup.cfg file. For example, Pillow provides for configuring available backends via additional build_ext command flags:

setup.py build_ext --enable-tiff --disable-webp ...

The respective options can be setup via the configuration file, where sections represent the commands and individual keys — options. Note that dashes need to be replaced by underscores, and flag-style options take boolean arguments. In this case, the ebuild can use:

src_configure() {
    cat >> setup.cfg <<-EOF
        disable_tiff = $(usex !tiff True False)
        enable_tiff = $(usex tiff True False)
        disable_webp = $(usex !webp True False)
        enable_webp = $(usex webp True False)

Calling custom setup.py commands

When working on packages using setuptools or modified distutils, you sometimes need to manually invoke setup.py. The eclass provides a esetup.py helper that wraps it with additional checks, error handling and ensures that the override configuration file is created beforehand (much like econf or emake).

esetup.py passes all its paremeters to ./setup.py.

python_test() {
    esetup.py check

Enabling tests

The support for test suites is now covered in the Tests in Python packages chapter.

Building documentation via Sphinx

dev-python/sphinx is commonly used to document Python packages. It comes with a number of plugins and themes that make it convenient to write and combine large text documents (such as this Guide!), as well as automatically document Python code.

Depending on the exact package, building documentation may range from being trivial to very hard. Packages that do not use autodoc (documenting of Python code) do not need to USE-depend on Sphinx at all. Packages that do that need to use a supported Python implementation for Sphinx, and packages that use plugins need to guarantee the same implementation across all plugins. To cover all those use cases easily, the distutils_enable_sphinx function is provided.

Basic documentation with autodoc

The most common case is a package that uses Sphinx along with autodoc. It can be recognized by conf.py listing sphinx.ext.autodoc in the extension list. In order to support building documentation, call distutils_enable_sphinx and pass the path to the directory containing Sphinx documentation:

 # Copyright 1999-2020 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2


 PYTHON_COMPAT=( python3_{6,7,8} )

 inherit distutils-r1

 DESCRIPTION="Colored stream handler for the logging module"

 KEYWORDS="~amd64 ~x86 ~amd64-linux ~x86-linux"


 distutils_enable_sphinx docs

This call takes care of it all: it adds doc USE flag to control building documentation, appropriate dependencies via the expert any-r1 API making it sufficient for Sphinx to be installed with only one of the supported implementations, and appropriate python_compile_all implementation to build and install HTML documentation.

Additional Sphinx extensions

It is not uncommon for packages to require additional third-party extensions to Sphinx. Those include themes. In order to specify dependencies on the additional packages, pass them as extra arguments to distutils_enable_sphinx.

 # Copyright 1999-2020 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2


 PYTHON_COMPAT=( pypy3 python3_{6,7,8} )
 inherit distutils-r1

 DESCRIPTION="Correctly inflect words and numbers"

 KEYWORDS="~amd64 ~arm64 ~ia64 ~ppc ~ppc64 ~x86"

 distutils_enable_sphinx docs \
     '>=dev-python/jaraco-packaging-3.2' \
     '>=dev-python/rst-linker-1.9' \

In this case, the function uses the any-r1 API to request one of the supported implementations to be enabled on all of those packages. However, it does not have to be the one in PYTHON_TARGETS for this package.

Sphinx without autodoc or extensions

Finally, there are packages that use Sphinx purely to build documentation from text files, without inspecting Python code. For those packages, the any-r1 API can be omitted entirely and plain dependency on dev-python/sphinx is sufficient. In this case, the --no-autodoc option can be specified instead of additional packages.

 # Copyright 1999-2020 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2


 PYTHON_COMPAT=( python2_7 python3_{6,7,8} )
 inherit distutils-r1

 DESCRIPTION="Python Serial Port extension"
 HOMEPAGE="https://github.com/pyserial/pyserial https://pypi.org/project/pyserial/"

 KEYWORDS="~alpha amd64 ~arm arm64 ~hppa ~ia64 ~m68k ~mips ~ppc ~ppc64 ~s390 ~sh ~sparc ~x86"

 distutils_enable_sphinx documentation --no-autodoc

Note that this is valid only if no third-party extensions are used. If additional packages need to be installed, the previous variant must be used instead.

The eclass tries to automatically determine whether --no-autodoc should be used, and issue a warning if it’s missing or incorrect.

Packages with optional Python build system usage

The eclass has been written with the assumption that the vast majority of its consumers will be using the Python build systems unconditionally. For this reason, it sets the ebuild metadata variables (dependencies, REQUIRED_USE) and exports phase functions by default. However, it also provides support for optional mode that can be used when Python is used conditionally to USE flags.

If DISTUTILS_OPTIONAL is set to a non-empty value, then the eclass does not alter ebuild metadata or export phase functions by default. The ebuild needs to declare appropriate dependencies and REQUIRED_USE explicitly, and call the appropriate phase functions.

The PYTHON_DEPS and PYTHON_REQUIRED_USE variables provided by the underlying Python eclasses should be used, as if using these eclasses directly. Furthermore, in PEP 517 mode an additional DISTUTILS_DEPS variable is exported that contains build-time dependnecies specific to wheel build and install, and should be added to BDEPEND.

At the very least, the phases having default sub-phase functions need to be called, that is:

  • distutils-r1_src_prepare

  • distutils-r1_src_compile

  • distutils-r1_src_install

Additional phases need to be called if the ebuild declares sub-phase functions for them.

Note that in optional mode, the default implementation of distutils-r1_python_prepare_all does not apply patches (to avoid collisions with other eclasses).


The distutils_enable_sphinx and distutils_enable_tests alter the ebuild metadata variables and declare sub-phase functions independently of the value of DISTUTILS_OPTIONAL. However, in order for the respective sub-phases to be executed the ebuild needs to call appropriate eclass phase functions (i.e. additionally call distutils-r1_src_test for the latter).

If unconditional test dependencies are undesirable, these functions cannot be used, and appropriate dependencies and sub-phases need to be declared explicitly.

In the legacy mode, the DISTUTILS_USE_SETUPTOOLS variable is not used if the optional mode is enabled. Instead, the dependency on dev-python/setuptools needs to be declared explicitly.

An example ebuild for a package utilizing autotools as a primary build system alongside a flit-based pyproject.toml in the top directory follows:

 # Copyright 1999-2022 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2


 PYTHON_COMPAT=( python3_{8..10} pypy3 )

 inherit distutils-r1

 # ...
 IUSE="python test"
     python? ( ${PYTHON_REQUIRED_USE} )"

     python? (
     python? (
         test? (

 src_prepare() {
     use python && distutils-r1_src_prepare

 src_compile() {
     use python && distutils-r1_src_compile

 python_test() {

 src_test() {
     use python && distutils-r1_src_test

 src_install() {
     use python && distutils-r1_src_install

Packages with Rust extensions (using Cargo)

Some Python build systems include support for writing extensions in the Rust programming language. Two examples of these are setuptools using dev-python/setuptools_rust plugin and Maturin. Normally, these build systems utilize the Cargo ecosystem to automatically download the Rust dependencies over the Internet. In Gentoo, cargo.eclass is used to provide these dependencies to ebuilds.

When creating a new ebuild for a package using Rust extensions or bumping one, you need to locate the Cargo.lock files within the package’s sources. Run pycargoebuild passing the list of the containing directories to generate a template ebuild, e.g.:

pycargoebuild /tmp/portage/dev-python/setuptools-rust-1.5.2/work/setuptools-rust-1.5.2/examples/*/

The actual ebuild inherits both cargo and distutils-r1 eclasses. Prior to inherit, CARGO_OPTIONAL should be used to avoid exporting phase functions, and CRATES should be declared. SRC_URI needs to contain URLs generated using cargo_crate_uris, and LICENSE the crate licenses in addition to the Python package’s license. QA_FLAGS_IGNORED needs to match all Rust extensions in order to prevent false positives on ignored CFLAGS and LDFLAGS warnings. Finally, the ebuild needs to call cargo_src_unpack.

Note that some Rust/Python packages use both Rust-level and Python-level tests. To check for this, it is a good idea to run cargo test manually and see if any tests are run. If they are, cargo_src_test should be called in python_test_all() (or possibly python_test() if they specifically use Python linkage).

An example ebuild follows:

 # Copyright 2022 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2


 PYTHON_COMPAT=( python3_{8..10} pypy3 )


 inherit cargo distutils-r1

 # ...

     $(cargo_crate_uris ${CRATES})

 LICENSE="|| ( BSD-2 Apache-2.0 )"
 # Crate licenses
 LICENSE+=" Apache-2.0 BSD BSD-2 MIT"


 # Rust does not respect CFLAGS/LDFLAGS

 src_unpack() {

 python_test_all() {
     cd src/rust || die

Installing packages without a PEP 517 build backend

The eclass features a special ‘no build system’ that is dedicated to packages that could benefit from distutils-r1 features yet either do not use a PEP 517-compliant build system, or cannot use one. This generally means that either:

  • it uses a non-PEP 517 build system (autotools, CMake, plain Meson)

  • it does not feature a build system at all

  • its build system cannot be used as that would cause cyclic dependencies during build backend bootstrap

This mode is not supposed to be used for legacy use of distutils or setuptools — these are handled via the setuptools backend.

The use cases for this mode partially overlap with the use of other Python eclasses, particularly python-single-r1. Using distutils-r1 is recommended if one of the eclass features benefits the particular ebuild, e.g. if Python modules are installed or one of the supported test runners are used. For pure bundles of Python scripts, python-single-r1 is preferable.

The ‘no build system’ mode is enabled via setting the following value:


When this mode is used, the following applies:

  • no dependencies on a build backend or PEP 517 machinery are declared (DISTUTILS_DEPS are empty)

  • the default implementation, distutils-r1_python_compile is a no-op

However, the following eclass features are still available:

  • Python interpreter dependencies, REQUIRED_USE and distutils-r1 phase functions are used (unless disabled via DISTUTILS_OPTIONAL)

  • the temporary venv is created in ${BUILD_DIR}/install for test phase to use (but the ebuild needs to install files there explicitly)

  • the contents of ${BUILD_DIR}/install are merged into ${D} by distutils-r1_python_install (if present; temporary venv files are removed)

  • distutils_enable_sphinx and distutils_enable_tests are functional

Installing packages manually into BUILD_DIR

The simplest approach towards installing packages manually is to use python_domodule in python_compile sub-phase. This causes the modules to be installed into ${BUILD_DIR}/install tree, effectively enabling them to be picked up for the test phase and merged in distutils-r1_python_install.

An example ebuild using a combination of GitHub archive (for tests) and PyPI wheel (for generated .dist-info) follows:


 PYTHON_COMPAT=( python3_{8..11} pypy3 )

 inherit distutils-r1

         -> ${P}.gh.tar.gz
         -> ${P}-py3-none-any.whl.zip


 distutils_enable_tests unittest

 python_compile() {
     python_domodule src/tomli "${WORKDIR}"/*.dist-info

Note that the wheel suffix is deliberately changed in order to enable automatic unpacking by the default src_unpack.

Installing packages manually into D

The alternative approach is to install files in python_install phase. This provides a greater number of helpers. However, the installed modules will not be provided in the venv for the test phase.

An example ebuild follows:


 PYTHON_COMPAT=( pypy3 python3_{8..11} )

 inherit distutils-r1

 distutils_enable_tests pytest

 python_install() {
     python_domodule gpep517
     python_newscript - gpep517 <<-EOF
         import sys
         from gpep517.__main__ import main

It is also valid to combine both approaches, e.g. install Python modules in python_compile, and scripts in python_install. In this case, distutils-r1_python_install needs to be called explicitly.

Integrating with a non-PEP 517 build system

The ‘no build system’ mode can also be used to use distutils-r1 sub-phases to integrate with a build system conveniently. The following ebuild fragment demonstrates using it with Meson:


PYTHON_COMPAT=( python3_{8..10} )

inherit meson distutils-r1

python_configure() {
    local emesonargs=(


python_compile() {

python_test() {

python_install() {