Packaging/Python

See Language-specific package helpers for a list of tools to package python packages.

Prepare Packaging

When you want to package a new software from a local checkout with the inputs coming from nixpkgs (and not virtualenv+pip) you can use the following shell.nix :

with import <nixpkgs> {};
with pkgs.python3Packages;

buildPythonPackage rec {
  name = "mypackage";
  src = ./path/to/source;
  propagatedBuildInputs = [ pytest numpy pkgs.libsndfile ];
}

You can now run nix-shell and it will drop you in a shell similar to the python setup.py develop mode which uses the local code in ./path/to/source as input. propagatedBuildInputs will contain the packages you need in your project. After you've finished developing you can replace the relative path with fetchFromGitHub { ... } or fetchPypi { ... }.

Pip and Virtualenv enabled nix-shell

It might be the case that you simply need to prototype fast small projects with pip and virtualenv without the need for relying on the dependencies being already packaged in nixpkgs. {{Notice|Keep in mind that the virtualenv symlinks will be invalidated if you update your system!||

For a local working python environment you can use the following shell.nix.

with import <nixpkgs> {};

stdenv.mkDerivation {
  name = "pip-env";
  buildInputs = [
    # System requirements.
    readline

    # Python requirements (enough to get a virtualenv going).
    python27Full
    python27Packages.virtualenv
    python27Packages.pip
  ];
  src = null;
  shellHook = ''
    # Allow the use of wheels.
    SOURCE_DATE_EPOCH=$(date +%s)

    # Augment the dynamic linker path
    export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:${R}/lib/R/lib:${readline}/lib
  '';
}

When invoked with nix-shell, this environment gives you a readline-enabled Python, plus virtualenv and pip, from which you can create a virtual environment and then proceed to fill it with pip-installed packages from requirements.txt or any other source of packages.

And the only other thing you need to do is figure out which non-Python packages your pip-installable packages will need, and include them in buildInputs.

Caveats

ModuleNotFoundError: No module named 'pkg_resources'

If you see this runtime error

ModuleNotFoundError: No module named 'pkg_resources'

add setuptools to your derivation

buildPythonPackage {
  # ...
  propagatedBuildInputs = [
    # ...
    setuptools
  ];
}

Please report such issues at https://github.com/NixOS/nixpkgs/issues

HTTP 404 with fetchPypi

example error:

curl: (22) The requested URL returned error: 404
error: cannot download stt-1.2.0.tar.gz from any mirror

when we look at https://pypi.org/project/stt/#files we see only *.whl files:

• stt-1.2.0-cp310-cp310-win_amd64.whl
• stt-1.2.0-cp310-cp310-manylinux_2_24_x86_64.whl
• stt-1.2.0-cp310-cp310-macosx_10_10_universal2.whl
• ...

this means, this is a binary release, so we have two options:

1. build from source
2. install binary release

build from source

replace this

    buildPythonPackage {
      pname = "TODO";
      version = "TODO";
      src = fetchPypi {
        inherit pname version;
        sha256 = ""; # TODO
      };

with this

    buildPythonPackage {
      pname = "TODO";
      version = "TODO";
      src = fetchFromGitHub {
        owner = "TODO";
        repo = "TODO";
        rev = "v${version}";
        sha256 = ""; # TODO
      };

install binary release

replace this

    buildPythonPackage {
      pname = "TODO";
      version = "TODO";
      src = fetchPypi {
        inherit pname version;
        sha256 = ""; # TODO
      };

with this

    buildPythonPackage {
      pname = "TODO";
      version = "TODO";
      format = "wheel";
      src = fetchPypi rec {
        inherit pname version format;
        sha256 = ""; # TODO
        dist = python;
        python = "py3";
        #abi = "none";
        #platform = "any";
      };

... or use fetchurl to download the *.whl file directly.
examples: grep for ".whl" in nixpkgs/pkgs/development/python-modules/

reference: fetchPypi implementation

setup.py

The setup.py file is required by buildPythonPackage, but it's missing in some packages

FileNotFoundError: [Errno 2] No such file or directory: 'setup.py'

If the package has a pyproject.toml file, set

buildPythonPackage {
  format = "pyproject";
}

If both setup.py and pyproject.toml are missing, you have to add one of these files, for example:

buildPythonPackage {
  preBuild = ''
    cat >setup.py <<'EOF'
    from setuptools import setup
    setup(
      name='someprogram',
      # ...
    )
    EOF
  '';
}

setup.py example:

from setuptools import setup

with open('requirements.txt') as f:
    install_requires = f.read().splitlines()

setup(
  name='someprogram',
  #packages=['someprogram'],
  version='0.1.0',
  #author='...',
  #description='...',
  install_requires=install_requires,
  scripts=[
    'someprogram.py',
  ],
  entry_points={
    # example: file some_module.py -> function main
    #'console_scripts': ['someprogram=some_module:main']
  },
)

scripts is useful for self-contained python scripts with no local imports.

If a python script has local imports, for example from .some_module import some_function, either include all files in the scripts array, or add only the entry function to entry_points.

In this example, someprogram.py would be installed as $out/bin/someprogram.py.
To rename the binary, for example to remove the .py file extension, you can use postInstall

buildPythonPackage {
  # ...
  postInstall = ''
    mv -v $out/bin/someprogram.py $out/bin/someprogram
  '';
}

requirements.txt

requirements.txt in it's simplest form is a list of python packages

numpy
Requests
Pillow

buildPythonPackage will check these dependencies, but you still must declare the nix dependencies in buildInputs, propagatedBuildInputs, checkInputs, ...

Automatic packaging

TODO https://github.com/nix-community/pip2nix

TODO https://github.com/nix-community/poetry2nix

TODO https://pypi.org/project/pypi2nix/

Testing via this command is deprecated

In most cases, tests will pass anyway and you can ignore the warning.

In some cases, tests will fail, for example:

running test
WARNING: Testing via this command is deprecated and will be removed in a future version. Users looking for a generic test entry point independent of test runner are encouraged to use tox.
[ ... ]
TypeError: some_function() missing 1 required positional argument: 'some_argument'

quick fix: run tests with python's unittest module

  checkPhase = ''
    runHook preCheck
    ${python.interpreter} -m unittest
    runHook postCheck
  '';

See also

• buildPythonPackage implementation
• Python in the nixpkgs manual
• Python on Nix is an "Extensive collection of Python projects from PyPI"
• Rust section of Nixpkgs manual - build Rust code in Python projects