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in pkgs.mkShell {
in pkgs.mkShell {
   packages = [
   packages = [
     (pkgs.python3.withPackages (python-pkgs: [
     (pkgs.python3.withPackages (python-pkgs: with python-pkgs; [
       # select Python packages here
       # select Python packages here
       python-pkgs.pandas
       pandas
       python-pkgs.requests
       requests
     ]))
     ]))
   ];
   ];
Line 27: Line 27:
In this example, we create a Python environment with packages <code>pandas</code> and <code>requests</code>.
In this example, we create a Python environment with packages <code>pandas</code> and <code>requests</code>.


You can find Python packages that are available in Nixpkgs using [https://search.nixos.org/packages search.nixos.org]. For instance, type a Python package name like <code>numpy</code> in the search bar and click on the search button on the right. You can narrow down results by clicking on eg. "python311Packages" in the "Package sets" section on the left. Note that in the snippet above, on lines 8 and 9, each package is listed in the form <code>python-pkgs.<name></code> where <code><name></code> corresponds to the one found in [https://search.nixos.org/packages search.nixos.org] . See [https://nix.dev/tutorials/nix-language.html Nix language basics] for more information on the <code>python-pkgs</code> attribute set.
You can find Python packages that are available in Nixpkgs using [https://search.nixos.org/packages search.nixos.org]. For instance, type a Python package name like <code>numpy</code> in the search bar and click on the search button on the right. You can narrow down results by clicking on eg. "python311Packages" in the "Package sets" section on the left. Note that in the snippet above, on lines 10-11, each package is listed in the form <code>python-pkgs.<name></code> where <code><name></code> corresponds to the one found in [https://search.nixos.org/packages search.nixos.org] . See [https://nix.dev/tutorials/nix-language.html Nix language basics] for more information on the <code>python-pkgs</code> attribute set.


Once you have picked the Python packages you want, run <code>nix-shell</code> (or <code>nix develop -f shell.nix</code>)  to build the Python environment and enter it. Once in the environment Python will be available in your PATH, so you can run eg. <code>python --version</code>.
Once you have picked the Python packages you want, run <code>nix-shell</code> (or <code>nix develop -f shell.nix</code>)  to build the Python environment and enter it. Once in the environment Python will be available in your PATH, so you can run eg. <code>python --version</code>.
Note that with NixOS, this method can be used to install packages at the system level, e.g. <syntaxhighlight lang="nix">
environment.systemPackages = with pkgs; [
  # ...
  (python3.withPackages (python-pkgs: with python-pkgs; [
      pandas
      requests
  ]))
];
</syntaxhighlight>
=== Using R packages in python with rpy2 ===
<syntaxhighlight lang="nix">
environment.systemPackages = with pkgs; [
  # ...
  (python3.withPackages (python-pkgs: with python-pkgs; [
      pandas
      requests
      rpy2
  ]))
  # don't use rWrapper.override
  rPackages.tidyverse
  rPackages.uwot
];
</syntaxhighlight>
=== Using Nix shell (new command line) ===
nix shell --impure --expr '(import <nixpkgs> {}).python3.withPackages (ps: with ps; [ swh-core swh-scanner ])'
If you don't use the channels any more, you can replace <code><nixpkgs></code> by an instance of the <code>NixOS/nixpkgs</code> repository using its absolute path.


==== Using a Python package not in Nixpkgs ====
==== Using a Python package not in Nixpkgs ====
Line 38: Line 69:
Generally, you may create a file that looks like this:<syntaxhighlight lang="nix" line="1">
Generally, you may create a file that looks like this:<syntaxhighlight lang="nix" line="1">
# toolz.nix
# toolz.nix
{ lib
{
, buildPythonPackage
  lib,
, fetchPypi
  buildPythonPackage,
, setuptools
  fetchPypi,
, wheel
  setuptools,
  wheel,
}:
}:


Line 71: Line 103:
   python = pkgs.python3.override {
   python = pkgs.python3.override {
     self = python;
     self = python;
     packageOverrides = pyself: pyfinal: {
     packageOverrides = pyfinal: pyprev: {
       toolz = pyfinal.callPackage ./toolz.nix { };
       toolz = pyfinal.callPackage ./toolz.nix { };
     };
     };
Line 87: Line 119:
}
}
</syntaxhighlight>Next time you enter the shell specified by this file, Nix will build and include the Python package you have written.
</syntaxhighlight>Next time you enter the shell specified by this file, Nix will build and include the Python package you have written.
==== Using nix-shell alongside pip  ====
When working on a collaborative python project you may want to be able to <code>pip install -r requirements.txt</code> if the project isn't packaged for nix specifically.


The problem is that a lot of python packages won't work out of the box when you pip install them.
=== Running Python packages which requires compilation and/or contains libraries precompiled without <code>nix</code> ===
To fix this issue, you can create a nix shell that will use <code>pip</code> for the packages that are installing properly, but will fix the environment for the packages that are causing issues.
 
If you want to use some Python packages containing libraries precompiled without <code>nix</code> as for example <code>[https://pypi.org/project/grpcio/ grpcio]</code> or <code>[https://pypi.org/project/numpy Numpy]</code>, you may encounter the following error :<syntaxhighlight lang="shell-session">
$ python -c 'import grpc'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/.../grpc/__init__.py", line 22, in <module>
    from grpc import _compression
  File "/.../grpc/_compression.py", line 20, in <module>
    from grpc._cython import cygrpc
ImportError: libstdc++.so.6: cannot open shared object file: No such file or directory


You can accomplish this by adding these two files to the root of your project:
</syntaxhighlight>This means that the Python package depends on compiled dynamically linked binaries that your NixOs environment fail to resolve.
<syntaxhighlight lang="nix" line="1">
# shell.nix
{ pkgs ? import <nixpkgs> {} }:


let
On NixOS, installing packages that need to compile code or use C libraries from outside of the <code>nix</code> package manager may fail if dependencies are not found in the expected locations. There are multiple ways to solve this, and most of them are just different ways for adding <code>/nix/store/...</code> to <code>$LD_LIBRARY_PATH</code>.
  # Choose your python version
  myPython = pkgs.python3;
  pythonPackages = pkgs.python3Packages;


  pythonWithPkgs = myPython.withPackages (pythonPkgs: with pythonPkgs; [
After doing one of the following, you should be able to install compiled libraries using <code>venv</code>, <code>poetry</code>, <code>uv</code>, <code>conda</code> or other packages managers.
    # This list contains tools for Python development.
    # You can also add other tools, like black.
    #
    # Note that even if you add Python packages here like PyTorch or Tensorflow,
    # they will be reinstalled when running `pip -r requirements.txt` because
    # virtualenv is used below in the shellHook.
    ipython
    pip
    setuptools
    virtualenvwrapper
    wheel
    black
  ]);


   extraBuildInputs = with pythonPackages; [
==== Using nix overlay ====
     # this list contains packages that you want to be available at runtime and might not be able to be installed properly via pip
<syntaxhighlight lang="nix">
    # pandas
{
    # requests
   nixpkgs.overlays = [(
  ] ++ (with pkgs; [
     self: super: rec {
    #
      # https://github.com/NixOS/nixpkgs/blob/c339c066b893e5683830ba870b1ccd3bbea88ece/nixos/modules/programs/nix-ld.nix#L44
  ]);
      # > We currently take all libraries from systemd and nix as the default.
in
      pythonldlibpath = lib.makeLibraryPath (with super; [
import ./python-shell.nix {
        zlib zstd stdenv.cc.cc curl openssl attr libssh bzip2 libxml2 acl libsodium util-linux xz systemd
  extraBuildInputs = extraBuildInputs;
      ]);
  # extraLibPackages = extraLibPackages;
      # here we are overriding python program to add LD_LIBRARY_PATH to it's env
  myPython = myPython;
      python = super.stdenv.mkDerivation {
   pythonWithPkgs = pythonWithPkgs;
        name = "python";
   pkgs = pkgs;
        buildInputs = [ super.makeWrapper ];
        src = super.python311;
        installPhase = ''
          mkdir -p $out/bin
          cp -r $src/* $out/
          wrapProgram $out/bin/python3 --set LD_LIBRARY_PATH ${pythonldlibpath}
          wrapProgram $out/bin/python3.11 --set LD_LIBRARY_PATH ${pythonldlibpath}
        '';
      };
      poetry = super.stdenv.mkDerivation {
        name = "poetry";
        buildInputs = [ super.makeWrapper ];
        src = super.poetry;
        installPhase = ''
          mkdir -p $out/bin
          cp -r $src/* $out/
          wrapProgram $out/bin/poetry --set LD_LIBRARY_PATH ${pythonldlibpath}
        '';
      };
    }
   )];
   environment.systemPackages = with pkgs; [
    python  # here python will be taken from the overlay up here
    poetry
  ];
}
}
</syntaxhighlight>
</syntaxhighlight>


<syntaxhighlight lang="nix" line="1">
==== Using [https://github.com/Mic92/nix-ld nix-ld] ====
# python-shell.nix
{ pkgs ? import <nixpkgs> {}, extraBuildInputs ? [], myPython ? pkgs.python3, extraLibPackages ? [], pythonWithPkgs? myPython }:


<syntaxhighlight lang="nix">
{
  programs.nix-ld = {
    enable = true;
    libraries = with pkgs; [
      zlib zstd stdenv.cc.cc curl openssl attr libssh bzip2 libxml2 acl libsodium util-linux xz systemd
    ];
  };
  # https://github.com/nix-community/nix-ld?tab=readme-ov-file#my-pythonnodejsrubyinterpreter-libraries-do-not-find-the-libraries-configured-by-nix-ld
  environment.systemPackages = [
    (pkgs.writeShellScriptBin "python" ''
      export LD_LIBRARY_PATH=$NIX_LD_LIBRARY_PATH
      exec ${pkgs.python3}/bin/python "$@"
    '')
  ];
  # another (dangerous) solution
  # environment.systemPackages = with pkgs; [ python3 ];
  # programs.bash = {
  #  enable = true;
  #  initExtra = ''
  #    export LD_LIBRARY_PATH=$LD_LIBRARY_PATH''${LD_LIBRARY_PATH:+:}$NIX_LD_LIBRARY_PATH
  #  '';
  # };
}
</syntaxhighlight>


let
==== Using [https://github.com/GuillaumeDesforges/fix-python/ fix-python] ====
{{Note|fix-python will <strong>patch</strong> binary files in the virtual environment without following symlinks.}}


    buildInputs  = with pkgs; [
Install with:
        clang
        llvmPackages_16.bintools
        rustup
    ] ++ extraBuildInputs;


  lib-path = with pkgs; lib.makeLibraryPath buildInputs;
<syntaxhighlight lang="shell">
nix profile install github:GuillaumeDesforges/fix-python
</syntaxhighlight>


Enter the venv and run:


shell = pkgs.mkShell {
<syntaxhighlight lang="shell">
  buildInputs = [
fix-python --venv .venv
    # my python and packages
</syntaxhighlight>
      pythonWithPkgs
     
      # other packages needed for compiling python libs
      pkgs.readline
      pkgs.libffi
      pkgs.openssl


      # unfortunately needed because of messing with LD_LIBRARY_PATH below
==== Using <code>buildFHSEnv</code> (Recommended) ====
      pkgs.git
<syntaxhighlight lang="nix">
      pkgs.openssh
#!/usr/bin/env nix-shell
      pkgs.rsync
{ pkgs ? import <nixpkgs> { } }:
  ] ++ extraBuildInputs;
(
   shellHook = ''
  let base = pkgs.appimageTools.defaultFhsEnvArgs; in
      # Allow the use of wheels.
   pkgs.buildFHSEnv (base // {
      SOURCE_DATE_EPOCH=$(date +%s)
    name = "FHS";
      # Augment the dynamic linker path
    targetPkgs = pkgs: (with pkgs; [
      export "LD_LIBRARY_PATH=$LD_LIBRARY_PATH:${lib-path}"
       gcc glibc zlib
      # Setup the virtual environment if it doesn't already exist.
    ]);
      VENV=.venv
    runScript = "zsh";
      if test ! -d $VENV; then
    extraOutputsToInstall = [ "dev" ];
        virtualenv $VENV
  })
       fi
).env
      source ./$VENV/bin/activate
      export PYTHONPATH=$PYTHONPATH:`pwd`/$VENV/${myPython.sitePackages}/
  '';
};
 
in
shell
</syntaxhighlight>
</syntaxhighlight>


=== Running compiled libraries ===
==== Using a custom nix-shell ====
If you want to run some compiled libraries as for example <code>grpcio</code><ref>https://pypi.org/project/grpcio/</ref>, you may encounter the following error :<syntaxhighlight lang="shell-session">
$ python -c 'import grpc'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/.../grpc/__init__.py", line 22, in <module>
    from grpc import _compression
  File "/.../grpc/_compression.py", line 20, in <module>
    from grpc._cython import cygrpc
ImportError: libstdc++.so.6: cannot open shared object file: No such file or directory
 
</syntaxhighlight>This means that the library use compiled dynamically linked binaries that your NixOs environment fail to resolve.
 
On NixOS, installing packages that need to compile code or use C libraries from outside of the <code>nix</code> package manager may fail if dependencies are not found in the expected locations.
There are multiple ways to make it work:
* Use [https://github.com/GuillaumeDesforges/fix-python/ fix-python], this is most suited for beginners.
 
* Create a FHS user env with <code>buildFHSUserEnv</code>.
* Setup <code>nix-ld</code><ref name=":0">https://github.com/Mic92/nix-ld</ref> in your NixOS configuration.
 
==== Setup nix-ld ====
nix-ld<ref name=":0" /> allow you to <code>Run unpatched dynamic binaries on NixOS.</code>


The following configuration automatically fix the dependencies :<syntaxhighlight lang="nixos" line="1">
The following configuration automatically fix the dependencies:<syntaxhighlight lang="nixos" line="1">
let
let
   python = pkgs.python311;
   python = pkgs.python311;
  # We currently take all libraries from systemd and nix as the default
   # https://github.com/NixOS/nixpkgs/blob/c339c066b893e5683830ba870b1ccd3bbea88ece/nixos/modules/programs/nix-ld.nix#L44
   # https://github.com/NixOS/nixpkgs/blob/c339c066b893e5683830ba870b1ccd3bbea88ece/nixos/modules/programs/nix-ld.nix#L44
  # > We currently take all libraries from systemd and nix as the default.
   pythonldlibpath = lib.makeLibraryPath (with pkgs; [
   pythonldlibpath = lib.makeLibraryPath (with pkgs; [
     zlib
     zlib zstd stdenv.cc.cc curl openssl attr libssh bzip2 libxml2 acl libsodium util-linux xz systemd
    zstd
    stdenv.cc.cc
    curl
    openssl
    attr
    libssh
    bzip2
    libxml2
    acl
    libsodium
    util-linux
    xz
    systemd
   ]);
   ]);
   patchedpython = (python.overrideAttrs (
   patchedpython = (python.overrideAttrs (
Line 263: Line 283:
in
in
{
{
  # Some other config...
 
   environment.systemPackages = with pkgs; [
   environment.systemPackages = with pkgs; [
     patchedpython
     patchedpython
     # if you want poetry
     # if you want poetry
     patchedpoetry
     patchedpoetry
Line 274: Line 291:
</syntaxhighlight>This configuration set the <code>LD_LIBRARY_PATH</code> environment variable before running python using the <code>overrideAttrs</code><ref>https://nixos.org/manual/nixpkgs/stable/#sec-pkg-overrideAttrs</ref> function to override the <code>postInstall</code> script of cpython <code>mkDerivation</code><ref>https://github.com/NixOS/nixpkgs/blob/24.05/pkgs/development/interpreters/python/cpython/default.nix</ref>.
</syntaxhighlight>This configuration set the <code>LD_LIBRARY_PATH</code> environment variable before running python using the <code>overrideAttrs</code><ref>https://nixos.org/manual/nixpkgs/stable/#sec-pkg-overrideAttrs</ref> function to override the <code>postInstall</code> script of cpython <code>mkDerivation</code><ref>https://github.com/NixOS/nixpkgs/blob/24.05/pkgs/development/interpreters/python/cpython/default.nix</ref>.


After this step, you should be able to install compiled libraries using venv, poetry, conda or other packages managers...
==== Prefix library paths using wrapProgram ====
wrapProgram is a part of the makeWrapper build input<ref>https://github.com/NixOS/nixpkgs/blob/master/pkgs/build-support/setup-hooks/make-wrapper.sh</ref>. By combining it with the symlinkJoin, we can create a wrapper around the Python executable that will always set the required library paths. It’s worth noting that, for this solution to be compatible with Darwin, we need to use a different wrap prefix, as shown in the example below.<syntaxhighlight lang="nixos" line="1">
let
  # We currently take all libraries from systemd and nix as the default
  # https://github.com/NixOS/nixpkgs/blob/c339c066b893e5683830ba870b1ccd3bbea88ece/nixos/modules/programs/nix-ld.nix#L44
  pythonldlibpath = lib.makeLibraryPath (with pkgs; [
    zlib zstd stdenv.cc.cc curl openssl attr libssh bzip2 libxml2 acl libsodium util-linux xz systemd
  ]);
  # Darwin requires a different library path prefix
  wrapPrefix = if (!pkgs.stdenv.isDarwin) then "LD_LIBRARY_PATH" else "DYLD_LIBRARY_PATH";
  patchedpython = (pkgs.symlinkJoin {
    name = "python";
    paths = [ pkgs.python312 ];
    buildInputs = [ pkgs.makeWrapper ];
    postBuild = ''
      wrapProgram "$out/bin/python3.12" --prefix ${wrapPrefix} : "${pythonldlibpath}"
    '';
  });
in
{
  environment.systemPackages = with pkgs; [
    patchedpython
  ];
}
</syntaxhighlight>


=== Using <code>venv</code> ===
=== Using <code>venv</code> ===
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$ nix-shell -p python3 --command "python -m venv .venv --copies"
$ nix-shell -p python3 --command "python -m venv .venv --copies"
</syntaxhighlight>You can then activate and use the Python virtual environment as usual and install dependencies with <code>pip</code> and similar.
</syntaxhighlight>You can then activate and use the Python virtual environment as usual and install dependencies with <code>pip</code> and similar.
=== Using uv ===
<blockquote>A single tool to replace <code>pip</code>, <code>pip-tools</code>, <code>pipx</code>, <code>poetry</code>, <code>pyenv</code>, <code>virtualenv</code>, and more.</blockquote>
uv is written in Rust and does ''not'' need Python as a prerequisite. Use the <code>uv</code> command to initialize Python projects, add Python packages, create or update virtual environments (in <code>.venv</code> folders), etc. as [https://docs.astral.sh/uv/concepts/projects/ described in the uv docs]. Use uv's [https://docs.astral.sh/uv/guides/tools/ tool interface] to install and run Python packages that provide a CLI.
As a system package
<syntaxhighlight lang="nix">
environment.systemPackages = with pkgs; [
    uv
];
</syntaxhighlight>
or as a home-manager package
<syntaxhighlight lang="nix">
home.packages = with pkgs; [
    uv
];
</syntaxhighlight>
If you use uv it's recommended that you install the Python versions you need using the <code>uv python install</code> command, e.g.
<syntaxhighlight lang="python">
uv python install 3.14 --preview --default
</syntaxhighlight>
You may want to set the <code>UV_PYTHON_DOWNLOADS=never</code> environment variable in your shell to stop uv from downloading Python binaries automatically if needed. Setting <code>environment.localBinInPath = true;</code> is highly recommended, because uv will install binaries in <code>~/.local/bin</code>.


=== Using poetry ===
=== Using poetry ===
Line 296: Line 366:
</syntaxhighlight>
</syntaxhighlight>


==== poetry2nix ====
[https://github.com/nix-community/poetry2nix poetry2nix] uses the contents of a <code>poetry.lock</code> and <code>pyproject.toml</code> file to create Nix derivations. It has several functions for generating development environments and python projects. Because some older python projects rely on deprecated build systems (see [https://github.com/nix-community/poetry2nix/blob/master/docs/edgecases.md edgecase.md] for more info), poetry2nix provides overrides so these packages can still be built.
=== Using micromamba ===
=== Using micromamba ===


Line 302: Line 374:
To activate an environment you will need a [https://nixos.org/manual/nixpkgs/stable/#sec-fhs-environments FHS environment] e.g.:
To activate an environment you will need a [https://nixos.org/manual/nixpkgs/stable/#sec-fhs-environments FHS environment] e.g.:
<syntaxhighlight lang="console">
<syntaxhighlight lang="console">
$ nix-shell -E 'with import <nixpkgs> {}; (pkgs.buildFHSUserEnv { name = "fhs"; }).env'
$ nix-shell -E 'with import <nixpkgs> {}; (pkgs.buildFHSEnv { name = "fhs"; }).env'
$ eval "$(micromamba shell hook -s bash)"
$ eval "$(micromamba shell hook -s bash)"
$ micromamba activate my-environment
$ micromamba activate my-environment
Line 313: Line 385:
{ pkgs ? import <nixpkgs> {}}:
{ pkgs ? import <nixpkgs> {}}:
let
let
   fhs = pkgs.buildFHSUserEnv {
   fhs = pkgs.buildFHSEnv {
     name = "my-fhs-environment";
     name = "my-fhs-environment";


Line 351: Line 423:
</syntaxhighlight>
</syntaxhighlight>
to set up conda in <code>~/.conda</code>
to set up conda in <code>~/.conda</code>
=== Using pixi ===
Install the <code>pixi</code> package to create environments and install packages as [https://pixi.sh/latest/ documented by pixi]:<syntaxhighlight lang="console">
$ pixi init
$ pixi add python
</syntaxhighlight>To activate an environment you will need a [https://nixos.org/manual/nixpkgs/stable/#sec-fhs-environments FHS environment] e.g. a [https://github.com/NixOS/nixpkgs/issues/316443#issuecomment-2151963505 flake.nix] <ref>Suggested flake.nix by [https://github.com/jonas-w @jonas-w] in response to '''[https://github.com/NixOS/nixpkgs/issues/316443 #316443 <bdi>Unable to add / run packages with pixi</bdi>]'''</ref><syntaxhighlight lang="nixos">
{
  description = "pixi env";
  inputs = {
    flake-utils.url = "github:numtide/flake-utils";
  };
  outputs =
    { flake-utils, nixpkgs, ... }:
    flake-utils.lib.eachDefaultSystem (
      system:
      let
        pkgs = import nixpkgs { inherit system; };
        fhs = pkgs.buildFHSEnv {
          name = "pixi-env";
          targetPkgs = _: [ pkgs.pixi ];
        };
      in
      {
        devShell = fhs.env;
      }
    );
}
</syntaxhighlight>Then using  <code>[https://wiki.nixos.org/wiki/Development_environment_with_nix-shell#nix_develop nix develop]</code> the environment can be activated:<syntaxhighlight lang="console">
$ nix develop
$ pixi s
$ python
>>> import numpy as np
</syntaxhighlight>
==== Using Home Manager ====
Alternatively an [https://nixos.org/manual/nixpkgs/stable/#sec-fhs-environments FHS environment] can wrap pixi using [[Home Manager]] e.g<ref>Suggested home manager config by [https://github.com/jennydaman @jennydaman] in response to '''[https://github.com/NixOS/nixpkgs/issues/316443 #316443 <bdi>Unable to add / run packages with pixi</bdi>]'''</ref><syntaxhighlight lang="nixos">
{ lib, pkgs, ... }:
{
  home.packages = [
    (pkgs.buildFHSEnv {
      name = "pixi";
      runScript = "pixi";
      targetPkgs = pkgs: with pkgs; [ pixi ];
    })
  ];
}
</syntaxhighlight>Then the environment can be activated:<syntaxhighlight lang="console">
$ pixi s
$ python
>>> import numpy as np
</syntaxhighlight>


== Package a Python application ==
== Package a Python application ==
It is possible to use <code>buildPythonApplication</code> to package python applications. As explained in the nixpkgs manual, it uses the widely used <code>setup.py</code> file in order to package properly the application. We now show how to package a simple python application: a basic flask web server.


First, we write the python code, say in a file <code>web_interface.py</code>. Here we create a basic flask web server:
=== With <code>setup.py</code> ===
To package a Python application that uses <code>setup.py</code> you can use <code>buildPythonApplication</code>. More details about this and similar functions can be found in [https://nixos.org/manual/nixpkgs/stable/#building-packages-and-applications the nixpkgs manual].
 
For example, we can package this simple flask server <code>main.py:</code>
<syntaxhighlight lang="python">
<syntaxhighlight lang="python">
#!/usr/bin/env python
#!/usr/bin/env python


from flask import Flask
from flask import Flask
app = Flask(__name__)
app = Flask(__name__)


Line 370: Line 497:
</syntaxhighlight>
</syntaxhighlight>


Then, we create the <code>setup.py</code> file, which basically explains which are the executables:
We also need a <code>setup.py</code> file, like this:
<syntaxhighlight lang="python">
<syntaxhighlight lang="python">
#!/usr/bin/env python
from setuptools import setup, find_packages
from setuptools import setup, find_packages


setup(name='demo-flask-vuejs-rest',
setup(name='myFlaskServer',
       version='1.0',
       version='1.0',
       # Modules to import from other scripts:
       # Modules to import from other scripts:
       packages=find_packages(),
       packages=find_packages(),
       # Executables
       # Executables
       scripts=["web_interface.py"],
       scripts=["main.py"],
     )
     )
</syntaxhighlight>
</syntaxhighlight>


Finally, our nix derivation is now trivial: the file <code>derivation.nix</code> just needs to provide the python packages (here flask):
Then, we use the <code>buildPythonApplication</code> in the <code>default.nix</code>:
<syntaxhighlight lang="nix">
<syntaxhighlight lang="nix">
{ lib, python3Packages }:
{ pkgs ? import <nixpkgs> {} }:
with python3Packages;
 
buildPythonApplication {
pkgs.python3Packages.buildPythonApplication {
   pname = "demo-flask-vuejs-rest";
   pname = "myFlaskApp";
   version = "1.0";
   version = "0.1.0";


   propagatedBuildInputs = [ flask ];
   propagatedBuildInputs = with pkgs.python3Packages; [
    flask
  ];


   src = ./.;
   src = ./.;
}
}
</syntaxhighlight>
</syntaxhighlight>Finally, build your project using <code>nix-build</code>. The result will be executable in <code>./result/bin/app.py</code>.
 
=== With <code>pyproject.toml</code> ===
When your project is using <code>pyproject.toml</code>you can use [https://github.com/nix-community/pyproject.nix pyproject.nix] to package your application.
 
First, a simple file structure could look like this:<syntaxhighlight>
├── app/
    └── main.py
├── flake.nix
├── pyproject.toml
└── README.md
 
 
</syntaxhighlight>To reuse the example from above, we use the same flask application:<syntaxhighlight lang="python">
from flask import Flask
 
app = Flask(__name__)
 
@app.route('/')
def hello_world():
    return 'Hello, World!'
 
if __name__ == '__main__':
    app.run(host="0.0.0.0", port=8080)
</syntaxhighlight>Also, you need to define the <code>pyproject.toml</code>. Here, we only show some of the important parts. Please refer to <code>pyproject.nix</code> [https://pyproject-nix.github.io/pyproject.nix/use-cases/pyproject.html documentation] for a full example.<syntaxhighlight lang="toml">
[project]
name = "my-app"
version = "0.1.0"
description = "Simple app"
 
# define any Python dependencies
dependencies = [
  "flask>3",
]
 
# define the CLI executable
# Here, we define the entry point to be the 'main()' function in the module 'app/main.py'
[project.scripts]
cli = "app.main:main"
</syntaxhighlight>We package the application by calling the <code>loadPyproject</code> function from <code>pyproject.nix</code>. Again, we only show a minimal example. More information can be found in the [https://pyproject-nix.github.io/pyproject.nix/use-cases/pyproject.html documentation]. Note that this example relies on flakes in contrast to some of the others on this page.<syntaxhighlight lang="nix">
{
  description = "A basic flake using pyproject.toml project metadata";
 
  inputs = {
    pyproject-nix = {
      url = "github:nix-community/pyproject.nix";
      inputs.nixpkgs.follows = "nixpkgs";
    };
  };
 
  outputs = { nixpkgs, pyproject-nix, ... }:
    let
      inherit (nixpkgs) lib;
 
      project = pyproject-nix.lib.project.loadPyproject {
        # Read & unmarshal pyproject.toml relative to this project root.
        # projectRoot is also used to set `src` for renderers such as buildPythonPackage.
        projectRoot = ./.;
      };
 
      # This example is only using x86_64-linux
      pkgs = nixpkgs.legacyPackages.x86_64-linux;
 
      python = pkgs.python3;
 
    in
    {
      # Build our package using `buildPythonPackage
      packages.x86_64-linux.default =
        let
          # Returns an attribute set that can be passed to `buildPythonPackage`.
          attrs = project.renderers.buildPythonPackage { inherit python; };
        in
        # Pass attributes to buildPythonPackage.
        # Here is a good spot to add on any missing or custom attributes.
        python.pkgs.buildPythonPackage (attrs // {
          env.CUSTOM_ENVVAR = "hello";
        });
    };
}


and we can now load this derivation from our file <code>default.nix</code>:
</syntaxhighlight>To run the application, call <code>nix run</code>.
<syntaxhighlight lang="nix">
{ pkgs ? import <nixpkgs> {} }:
pkgs.callPackage ./derivation.nix {}
</syntaxhighlight>


We can now build with:
You can also launch an IDE under <code>nix develop</code> and get full dependency resolution. For example, the following command opens VS Code in the constructed environment:
<syntaxhighlight lang=console>
$ nix-build
[...]
$ ./result/bin/web_interface.py
* Serving Flask app ".web_interface" (lazy loading)
[...]
</syntaxhighlight>
or just enter a nix-shell, and directly execute your program or python if it's easier to develop:
<syntaxhighlight lang=console>
$ nix-shell
[...]
[nix-shell]$ chmod +x web_interface.py
[nix-shell]$ ./web_interface.py
* Serving Flask app "web_interface" (lazy loading)
[...]


[nix-shell]$ python
<syntaxhighlight lang="shell-session">
Python 3.8.7 (default, Dec 21 2020, 17:18:55)
$ nix develop --command code
[GCC 10.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import flask
>>>
</syntaxhighlight>
</syntaxhighlight>


Line 449: Line 632:


<syntaxhighlight lang="nix" line="1">
<syntaxhighlight lang="nix" line="1">
{ lib
{
, pythonPackages
  lib,
  pythonPackages,
}:
}:
buildPythonApplication {
buildPythonApplication {
Line 479: Line 663:


You can also set <code>backend : GTK3Agg</code> in your <code>~/.config/matplotlib/matplotlibrc</code> file to avoid having to call <code>matplotlib.use('gtk3agg')</code>.
You can also set <code>backend : GTK3Agg</code> in your <code>~/.config/matplotlib/matplotlibrc</code> file to avoid having to call <code>matplotlib.use('gtk3agg')</code>.
== Debug Build ==
See [https://docs.python.org/3/using/configure.html#python-debug-build python wiki on debug build].
In order to use a CPython interpreter built using <code>--with-pydebug</code> during configure phase, override any of the python packages passing <code>enableDebug = true</code> argument:
<code>pythonDebug = pkgs.python310.override { enableDebug = true; };</code>
== Installing Multiple Versions ==
{{Nixpkgs Manual|name={{ic|lib.meta.lowPrio}} and {{ic|lib.meta.highPrio}}|anchor=#function-library-lib.meta.lowPrio}} can be used to install multiple versions without conflicts ({{issue|369997}}):
{{file|/etc/nixos/configuration.nix|nix|3=
environment.systemPackages = with pkgs; [
    python313
    lib.meta.lowPrio python314
];
}}
In this case you may run Python 3.13 via {{ic|python}} or {{ic|python3.13}} and Python 3.14 via {{ic|python3.14}}.
{{Note|If you wrapped Python as described in [[#Running_Python_packages_which_requires_compilation_and/or_contains_libraries_precompiled_without_nix]], call {{ic|lib.meta.lowPrio}} and {{ic|lib.meta.highPrio}} for the wrapped Python instead of calling them inside the wrapping.}}


== Performance ==
== Performance ==
Line 521: Line 727:
* [https://nixos.org/manual/nixpkgs/unstable/#python "Python" in Nixpkgs Manual]
* [https://nixos.org/manual/nixpkgs/unstable/#python "Python" in Nixpkgs Manual]
[[Category:Languages]]
[[Category:Languages]]
[[Category:Python]]
Retrieved from "https://wiki.nixos.org/wiki/Python"