Python
Currently supported interpreters are python26, python27,
python33, python34, python35
and pypy.
python is an alias to python27 and python3 is an alias to python34.
python26 and python27 do not include modules that require
external dependencies (to reduce dependency bloat). Following modules need to be added as
buildInput explicitly:
python.modules.bsddbpython.modules.cursespython.modules.curses_panelpython.modules.cryptpython.modules.gdbmpython.modules.sqlite3python.modules.tkinterpython.modules.readlineFor convenience python27Full and python26Full
are provided with all modules included.
Python packages that
use setuptools or distutils,
can be built using the buildPythonPackage function as documented below.
All packages depending on any Python interpreter get appended $out/${python.sitePackages}
to $PYTHONPATH if such directory exists.
Useful attributes on interpreters packages:
libPrefix
Name of the folder in ${python}/lib/ for corresponding interpreter.
interpreter
Alias for ${python}/bin/${executable}.buildEnv
Function to build python interpreter environments with extra packages bundled together.
See for usage and documentation.
sitePackages
Alias for lib/${libPrefix}/site-packages.
executable
Name of the interpreter executable, ie python3.4.
<varname>buildPythonPackage</varname> function
The function is implemented in
pkgs/development/python-modules/generic/default.nix.
Example usage:
twisted = buildPythonPackage {
name = "twisted-8.1.0";
src = pkgs.fetchurl {
url = http://tmrc.mit.edu/mirror/twisted/Twisted/8.1/Twisted-8.1.0.tar.bz2;
sha256 = "0q25zbr4xzknaghha72mq57kh53qw1bf8csgp63pm9sfi72qhirl";
};
propagatedBuildInputs = [ self.ZopeInterface ];
meta = {
homepage = http://twistedmatrix.com/;
description = "Twisted, an event-driven networking engine written in Python";
license = stdenv.lib.licenses.mit;
};
};
Most of Python packages that use buildPythonPackage are defined
in pkgs/top-level/python-packages.nix
and generated for each python interpreter separately into attribute sets python26Packages,
python27Packages, python35Packages, python33Packages,
python34Packages and pypyPackages.
buildPythonPackage mainly does four things:
In the buildPhase, it calls
${python.interpreter} setup.py bdist_wheel to build a wheel binary zipfile.
In the installPhase, it installs the wheel file using
pip install *.whl.
In the postFixup phase, wrapPythonPrograms
bash function is called to wrap all programs in $out/bin/*
directory to include $PYTHONPATH and $PATH
environment variables.
In the installCheck phase, ${python.interpreter} setup.py test
is ran.
By default doCheck = true is set
As in Perl, dependencies on other Python packages can be specified in the
buildInputs and
propagatedBuildInputs attributes. If something is
exclusively a build-time dependency, use
buildInputs; if it’s (also) a runtime dependency,
use propagatedBuildInputs.
By default meta.platforms is set to the same value
as the interpreter unless overriden otherwise.
<varname>buildPythonPackage</varname> parameters
(all parameters from <varname>mkDerivation</varname> function are still supported)
namePrefix
Prepended text to ${name} parameter.
Defaults to "python3.3-" for Python 3.3, etc. Set it to
""
if you're packaging an application or a command line tool.
disabled
If true, package is not build for
particular python interpreter version. Grep around
pkgs/top-level/python-packages.nix
for examples.
setupPyBuildFlags
List of flags passed to setup.py build_ext command.
pythonPath
List of packages to be added into $PYTHONPATH.
Packages in pythonPath are not propagated
(contrary to propagatedBuildInputs).
preShellHook
Hook to execute commands before shellHook.
postShellHook
Hook to execute commands after shellHook.
makeWrapperArgs
A list of strings. Arguments to be passed to
makeWrapper, which wraps generated binaries. By
default, the arguments to makeWrapper set
PATH and PYTHONPATH environment
variables before calling the binary. Additional arguments here can
allow a developer to set environment variables which will be
available when the binary is run. For example,
makeWrapperArgs = ["--set FOO BAR" "--set BAZ QUX"].
<function>python.buildEnv</function> function
Create Python environments using low-level pkgs.buildEnv function. Example default.nix:
{};
python.buildEnv.override {
extraLibs = [ pkgs.pythonPackages.pyramid ];
ignoreCollisions = true;
}]]>
Running nix-build will create
/nix/store/cf1xhjwzmdki7fasgr4kz6di72ykicl5-python-2.7.8-env
with wrapped binaries in bin/.
You can also use env attribute to create local
environments with needed packages installed (somewhat comparable to
virtualenv). For example, with the following
shell.nix:
{};
(python3.buildEnv.override {
extraLibs = with python3Packages;
[ numpy
requests
];
}).env]]>
Running nix-shell will drop you into a shell where
python will have specified packages in its path.
<function>python.buildEnv</function> arguments
extraLibs
List of packages installed inside the environment.
postBuild
Shell command executed after the build of environment.
ignoreCollisions
Ignore file collisions inside the environment (default is false).
ToolsPackages inside nixpkgs are written by hand. However many tools
exist in community to help save time. No tool is preferred at the moment.
python2nix
by Vladimir Kirillov
pypi2nix
by Rok Garbas
pypi2nix
by Jaka Hudoklin
Development
To develop Python packages buildPythonPackage has
additional logic inside shellPhase to run
pip install -e . --prefix $TMPDIR/ for the package.
shellPhase is executed only if setup.py
exists.
Given a default.nix:
{};
buildPythonPackage {
name = "myproject";
buildInputs = with pkgs.pythonPackages; [ pyramid ];
src = ./.;
}]]>
Running nix-shell with no arguments should give you
the environment in which the package would be build with
nix-build.
Shortcut to setup environments with C headers/libraries and python packages:
$ nix-shell -p pythonPackages.pyramid zlib libjpeg git
There is a boolean value lib.inNixShell set to
true if nix-shell is invoked.
FAQHow to solve circular dependencies?
If you have packages A and B that
depend on each other, when packaging B override package
A not to depend on B as input
(and also the other way around).
install_data / data_files problems resulting into error: could not create '/nix/store/6l1bvljpy8gazlsw2aw9skwwp4pmvyxw-python-2.7.8/etc': Permission denied
Known bug in setuptools install_data does not respect --prefix. Example of
such package using the feature is pkgs/tools/X11/xpra/default.nix. As workaround
install it as an extra preInstall step:
${python.interpreter} setup.py install_data --install-dir=$out --root=$out
sed -i '/ = data_files/d' setup.pyRationale of non-existent global site-packages
There is no need to have global site-packages in Nix. Each package has isolated
dependency tree and installing any python package will only populate $PATH
inside user environment. See to create self-contained
interpreter with a set of packages.
Contributing guidelines
Following rules are desired to be respected:
Make sure package builds for all python interpreters. Use disabled argument to
buildPythonPackage to set unsupported interpreters.
If tests need to be disabled for a package, make sure you leave a comment about reasoning.
Packages in pkgs/top-level/python-packages.nix
are sorted quasi-alphabetically to avoid merge conflicts.