Advanced dependencies¶
Requesting USE flags on the Python interpreter¶
While the majority of Python standard library modules are available
unconditionally, a few are controlled by USE flags. For example,
the sqlite3 module requires sqlite
flag to be enabled
on the interpreter. If a package requires this module, it needs
to enforce the matching flag via a USE dependency.
In order to create a USE dependency on the Python interpreter, set
PYTHON_REQ_USE
before inheriting the eclass. This will cause
the eclass to generate appropriate dependency string in PYTHON_DEPS
.
# Copyright 1999-2020 Gentoo Authors
# Distributed under the terms of the GNU General Public License v2
EAPI=7
PYTHON_COMPAT=( python3_6 )
PYTHON_REQ_USE="sqlite"
inherit python-r1 gnome2-utils meson xdg-utils
DESCRIPTION="Modern music player for GNOME"
HOMEPAGE="https://wiki.gnome.org/Apps/Lollypop"
SRC_URI="https://adishatz.org/${PN}/${P}.tar.xz"
KEYWORDS="~amd64"
LICENSE="GPL-3"
SLOT="0"
REQUIRED_USE=${PYTHON_REQUIRED_USE}
DEPEND="${PYTHON_DEPS}
..."
Full USE dependency syntax is permitted. For example, you can make the dependency conditional to a flag on the package:
# Copyright 1999-2020 Gentoo Authors
# Distributed under the terms of the GNU General Public License v2
EAPI=6
PYTHON_COMPAT=( python3_6 )
PYTHON_REQ_USE="sqlite?"
inherit distutils-r1
DESCRIPTION="A lightweight password-manager with multiple database backends"
HOMEPAGE="https://pwman3.github.io/pwman3/"
SRC_URI="https://github.com/pwman3/pwman3/archive/v${PV}.tar.gz -> ${P}.tar.gz"
LICENSE="GPL-3"
SLOT="0"
KEYWORDS="~amd64"
IUSE="mongodb mysql postgres +sqlite"
Finally, there are cases when the problem cannot be fully solved using
a single USE dependency. Additional Python interpreter dependencies
with specific USE flags can be constructed using python_gen_impl_dep
helper then. For example, the following ebuild requires Python with
SQLite support when running tests:
# Copyright 1999-2020 Gentoo Authors
# Distributed under the terms of the GNU General Public License v2
EAPI=7
PYTHON_COMPAT=( python{2_7,3_{6,7,8}} pypy3 )
inherit distutils-r1
DESCRIPTION="Let your Python tests travel through time"
HOMEPAGE="https://github.com/spulec/freezegun"
SRC_URI="mirror://pypi/${PN:0:1}/${PN}/${P}.tar.gz"
LICENSE="Apache-2.0"
SLOT="0"
KEYWORDS="~alpha ~amd64 ~arm ~arm64 ~hppa ~ia64 ~m68k ~mips ~ppc ~ppc64 ~s390 ~sh ~sparc ~x86 ~amd64-linux ~x86-linux ~ppc-macos ~x64-macos ~x86-macos"
RDEPEND="
>dev-python/python-dateutil-2.0[${PYTHON_USEDEP}]
dev-python/six[${PYTHON_USEDEP}]
"
DEPEND="${RDEPEND}
dev-python/setuptools[${PYTHON_USEDEP}]
test? (
$(python_gen_impl_dep sqlite)
dev-python/mock[${PYTHON_USEDEP}]
dev-python/nose[${PYTHON_USEDEP}]
)
"
distutils_enable_tests pytest
Dependencies conditional to Python version¶
When packaging software for multiple Python versions, it is quite likely that you’ll find yourself needing some packages only with some of the versions, and not with others. This is the case with backports and other compatibility packages. It also happens if some of the optional dependencies do not support the full set of implementations your package supports.
A dependency that applies only to a subset of PYTHON_COMPAT
can
be created using python_gen_cond_dep
function (the same as used
in python-single-r1
). It takes a dependency string template,
followed by zero or more implementation arguments. The dependencies
are output for every matching implementation.
The dependency template should contain literal (usually escaped through
use of single quotes) ${PYTHON_USEDEP}
that will be substituted
with partial USE dependency by the eclass function (when using
python-single-r1
, ${PYTHON_SINGLE_USEDEP}
is also permitted).
The implementation arguments can be:
Literal implementation names. For example, if a particular feature is only available on a subset of Python implementations supported by the package:
RDEPEND=" cli? ( $(python_gen_cond_dep ' dev-python/black[${PYTHON_USEDEP}] dev-python/click[${PYTHON_USEDEP}] ' python3_{8..10}) ) "
fnmatch(3)
-style wildcard against implementation names. For example, CFFI is part of PyPy’s stdlib, so the explicit package needs to be only installed for CPython:RDEPEND=" $(python_gen_cond_dep ' dev-python/cffi[${PYTHON_USEDEP}] ' 'python*') "
Remember that the patterns need to be escaped to prevent filename expansion from happening.
Python standard library versions that are expanded into appropriate implementations by the eclass. For example, this makes it convenient to depend on backports:
RDEPEND=" $(python_gen_cond_dep ' dev-python/backports-zoneinfo[${PYTHON_USEDEP}] ' 3.8) "
The advantage of this form is that the dependencies automatically adjust as we switch PyPy3 to a newer stdlib version.
An important feature of python_gen_cond_dep
is that it handles
removal of old implementations gracefully. When one of the listed
implementations is no longer supported, it silently ignores it. This
makes it possible to remove old implementations without having to update
all dependency strings immediately.
For example, in the following example the dependency became empty when Python 3.7 was removed:
RDEPEND="
$(python_gen_cond_dep '
dev-python/importlib_metadata[${PYTHON_USEDEP}]
' python3_7)"
Dependencies on CFFI and greenlet¶
The PyPy distribution includes special versions of the cffi and greenlet packages. For this reason, packages using CFFI and/or greenlet and supporting PyPy3 need to make the explicit dependencies conditional to CPython:
RDEPEND="
$(python_gen_cond_dep '
>=dev-python/cffi-1.1.0:=[${PYTHON_USEDEP}]
' 'python*')
"