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 ^[1]:

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^[2].

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

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

build from source
install binary release

build from source

replace this

      src = fetchPypi {
        inherit pname version;
        sha256 = "";
      };

with this

      src = fetchFromGitHub {
        owner = "todo";
        repo = "todo";
        rev = "todo";
        sha256 = "";
      };

install binary release

TODO

examples: grep for ".whl" in nixpkgs/pkgs/development/python-modules/

TODO or use buildPythonPackage { format = "wheel"; }?

setup.py

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

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={
    #'console_scripts': ['someprogram=some_module:main']
  },
)

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/poetry2nix

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

References

[1] xpkgs manual

[2] ttps://groups.google.com/forum/#!topic/nix-devel/3qPfwCAV3GE

[1]

[2]