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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 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 ====
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   };
   };
   # https://github.com/nix-community/nix-ld?tab=readme-ov-file#my-pythonnodejsrubyinterpreter-libraries-do-not-find-the-libraries-configured-by-nix-ld
   # https://github.com/nix-community/nix-ld?tab=readme-ov-file#my-pythonnodejsrubyinterpreter-libraries-do-not-find-the-libraries-configured-by-nix-ld
  # https://github.com/search?q=%22export+LD_LIBRARY_PATH%3D%24NIX_LD_LIBRARY_PATH%22+python&type=code
   environment.systemPackages = [
   environment.systemPackages = [
     (pkgs.writeShellScriptBin "python" ''
     (pkgs.writeShellScriptBin "python" ''
       export LD_LIBRARY_PATH=$NIX_LD_LIBRARY_PATH
       export LD_LIBRARY_PATH=$NIX_LD_LIBRARY_PATH
       exec ${pkgs.python311}/bin/python "$@"
       exec ${pkgs.python3}/bin/python "$@"
     '')
     '')
   ];
   ];
   # another dangerous but simple solution
   # another (dangerous) solution
  # https://github.com/nix-community/nix-ld?tab=readme-ov-file#why-not-set-ld_library_path-directly-instead-of-nix_ld_library_path
   # environment.systemPackages = with pkgs; [ python3 ];
   # environment.systemPackages = with pkgs; [ python311 poetry ];
   # programs.bash = {
   # programs.bash = {
   #  enable = true;
   #  enable = true;
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</syntaxhighlight>
</syntaxhighlight>


==== Using <code>buildFHSEnv</code> ====
==== Using <code>buildFHSEnv</code> (Recommended) ====
<syntaxhighlight lang="nix">
<syntaxhighlight lang="nix">
#!/usr/bin/env nix-shell
#!/usr/bin/env nix-shell
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=== Using uv ===
=== 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 very simple to use. Simply <code>uv init</code> to get started. No need for shells, as it creates virtual environments.
<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


As a systemPackage<syntaxhighlight lang="nix">
<syntaxhighlight lang="nix">
environment.systemPackages = with pkgs; [
environment.systemPackages = with pkgs; [
     uv
     uv
];
];
</syntaxhighlight>or as a home-manager package<syntaxhighlight lang="nix">
</syntaxhighlight>
 
or as a home-manager package
 
<syntaxhighlight lang="nix">
home.packages = with pkgs; [
home.packages = with pkgs; [
     uv
     uv
];
];
</syntaxhighlight>
</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 ===
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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
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{ pkgs ? import <nixpkgs> {}}:
{ pkgs ? import <nixpkgs> {}}:
let
let
   fhs = pkgs.buildFHSUserEnv {
   fhs = pkgs.buildFHSEnv {
     name = "my-fhs-environment";
     name = "my-fhs-environment";


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       let
       let
         pkgs = import nixpkgs { inherit system; };
         pkgs = import nixpkgs { inherit system; };
         fhs = pkgs.buildFHSUserEnv {
         fhs = pkgs.buildFHSEnv {
           name = "pixi-env";
           name = "pixi-env";


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{
{
   home.packages = [
   home.packages = [
     (pkgs.buildFHSUserEnv {
     (pkgs.buildFHSEnv {
       name = "pixi";
       name = "pixi";
       runScript = "pixi";
       runScript = "pixi";
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if __name__ == '__main__':
if __name__ == '__main__':
     app.run(host="0.0.0.0", port=8080)
     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://nix-community.github.io/pyproject.nix/use-cases/pyproject.html documentation] for a full example.<syntaxhighlight lang="toml">
</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]
[project]
name = "my-app"
name = "my-app"
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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 ==
Retrieved from "https://wiki.nixos.org/wiki/Python"