Python - Revision history

DHCP: /* Using nix-ld */ use for shell commands

2026-06-01T11:19:44Z

Using nix-ld: use <syntaxhighlight lang=console> for shell commands

← Older revision		Revision as of 11:19, 1 June 2026
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	];		];
	}		}
	</syntaxhighlight>Then, you can use your own pythonld in a specific virtual env like:<syntaxhighlight lang="~~bash~~">		</syntaxhighlight>Then, you can use your own pythonld in a specific virtual env like:<syntaxhighlight lang="console">
	$ pythonld -m venv myvenv		$ pythonld -m venv myvenv
	$ source myvenv/bin/activate		$ source myvenv/bin/activate
Line 255:		Line 255:
	];		];
	}		}
	</syntaxhighlight>And then use it like:<syntaxhighlight lang="~~bash~~">		</syntaxhighlight>And then use it like:<syntaxhighlight lang="console">
	$ pythonld -m venv --system-site-packages myvenv		$ pythonld -m venv --system-site-packages myvenv
	$ source myvenv/bin/activate		$ source myvenv/bin/activate

TobiasBora: /* Using nix-ld */ Add system-wide packages

2026-06-01T07:28:48Z

Using nix-ld: Add system-wide packages

@@ Line 230: / Line 230: @@
 </syntaxhighlight>Then, you can use your own pythonld in a specific virtual env like:<syntaxhighlight lang="bash">
 $ pythonld -m venv myvenv
 $ source myvenv/bin/activate
 $ pip install …

TobiasBora: /* Using nix-ld */ Explain how to use python with a venv

2026-06-01T07:18:40Z

Using nix-ld: Explain how to use python with a venv

@@ Line 195: / Line 195: @@
      (pkgs.writeShellScriptBin "python" ''
        export LD_LIBRARY_PATH=$NIX_LD_LIBRARY_PATH
-       exec ${pkgs.python3}/bin/python "$@"
+       exec -a "$0" ${pkgs.python3}/bin/python "$@"
      '')
    ];
@@ Line 207: / Line 207: @@
    # };
+}
 </syntaxhighlight>

DHCP: /* Regression */ remove unneeded text from command samples

2026-05-20T21:43:19Z

Regression: remove unneeded text from command samples

← Older revision		Revision as of 21:43, 20 May 2026
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	=== Regression ===		=== Regression ===
	With the <code>nixpkgs</code> version of Python you can expect anywhere from a 30-40% regression on synthetic benchmarks. For example:		With the <code>nixpkgs</code> version of Python you can expect anywhere from a 30-40% regression on synthetic benchmarks. For example:
	<syntaxhighlight lang=console>## Ubuntu's Python 3.8		<syntaxhighlight lang=console>
	~~username:dir~~$ python3.8 -c "import timeit; print(timeit.Timer('for i in range(100): oct(i)', 'gc.enable()').repeat(5))"		## Ubuntu's Python 3.8
			$ python3.8 -c "import timeit; print(timeit.Timer('for i in range(100): oct(i)', 'gc.enable()').repeat(5))"
	[7.831622750498354, 7.82998560462147, 7.830805554986, 7.823807033710182, 7.84282516874373]		[7.831622750498354, 7.82998560462147, 7.830805554986, 7.823807033710182, 7.84282516874373]

	## nix-shell's Python 3.8		## nix-shell's Python 3.8
	[nix-shell:~~~/src~~]$ python3.8 -c "import timeit; print(timeit.Timer('for i in range(100): oct(i)', 'gc.enable()').repeat(5))"		[nix-shell:~]$ python3.8 -c "import timeit; print(timeit.Timer('for i in range(100): oct(i)', 'gc.enable()').repeat(5))"
	[10.431915327906609, 10.435049421153963, 10.449542525224388, 10.440207410603762, 10.431304694153368]		[10.431915327906609, 10.435049421153963, 10.449542525224388, 10.440207410603762, 10.431304694153368]
	</syntaxhighlight>		</syntaxhighlight>

	However, synthetic benchmarks are not necessarily reflective of real-world performance. In common real-world situations, the performance difference between optimized and non-optimized interpreters is minimal. For example, using <code>pylint</code> with a significant number of custom linters to scan a very large Python codebase (>6000 files) resulted in only a 5.5% difference. Other workflows that were not performance sensitive saw no impact to their run times.		However, synthetic benchmarks are not necessarily reflective of real-world performance. In common real-world situations, the performance difference between optimized and non-optimized interpreters is minimal. For example, using <code>pylint</code> with a significant number of custom linters to scan a very large Python codebase (>6000 files) resulted in only a 5.5% difference. Other workflows that were not performance sensitive saw no impact to their run times.

	=== Possible Optimizations ===		=== Possible Optimizations ===
	If you run code that heavily depends on Python performance, and you desire the most performant Python interpreter possible, here are some possible things you can do:		If you run code that heavily depends on Python performance, and you desire the most performant Python interpreter possible, here are some possible things you can do:

DHCP: improve syntax highlighting, prefix shell commands with "$"

2026-05-20T21:38:56Z

improve syntax highlighting, prefix shell commands with "$"

← Older revision		Revision as of 21:38, 20 May 2026
Line 59:		Line 59:

	=== Using Nix shell (new command line) ===		=== Using Nix shell (new command line) ===
	nix shell --impure --expr '(import <nixpkgs> {}).python3.withPackages (ps: with ps; [ swh-core swh-scanner ])'		<syntaxhighlight lang="console">
			$ nix shell --impure --expr '(import <nixpkgs> {}).python3.withPackages (ps: with ps; [ swh-core swh-scanner ])'
			</syntaxhighlight>
	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.		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.

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	</syntaxhighlight>		</syntaxhighlight>

	==== Using [https://github.com/~~Mic92~~/nix-ld nix-ld] ====		==== Using [https://github.com/nix-community/nix-ld nix-ld] ====

	<syntaxhighlight lang="nix">		<syntaxhighlight lang="nix">
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	Install with:		Install with:

	<syntaxhighlight lang="~~shell~~">		<syntaxhighlight lang="console">
	nix profile install github:GuillaumeDesforges/fix-python		$ nix profile install github:GuillaumeDesforges/fix-python
	</syntaxhighlight>		</syntaxhighlight>

	Enter the venv and run:		Enter the venv and run:

	<syntaxhighlight lang="~~shell~~">		<syntaxhighlight lang="console">
	fix-python --venv .venv		$ fix-python --venv .venv
	</syntaxhighlight>		</syntaxhighlight>

Line 346:		Line 348:
	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.		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~~">		<syntaxhighlight lang="console">
	uv python install 3.14 --preview --default		$ uv python install 3.14 --preview --default
	</syntaxhighlight>		</syntaxhighlight>

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	In this case use a <code>nix-shell</code> with <code>gobject-introspection</code> and all the libraries you are using (gtk and so on) as <code>buildInputs</code>.		In this case use a <code>nix-shell</code> with <code>gobject-introspection</code> and all the libraries you are using (gtk and so on) as <code>buildInputs</code>.
	For example:		For example:
	~~{{Commands\|~~<~~nowiki~~>$ nix-shell -p gobjectIntrospection gtk3 'python2.withPackages (ps: with ps; [ pygobject3 ])' --run "python -c \"import pygtkcompat; pygtkcompat.enable_gtk(version='3.0')\""</~~nowiki~~>}}		<syntaxhighlight lang=console>
			$ nix-shell -p gobjectIntrospection gtk3 'python2.withPackages (ps: with ps; [ pygobject3 ])' --run "python -c \"import pygtkcompat; pygtkcompat.enable_gtk(version='3.0')\""
			</syntaxhighlight>

	Or, if you want to use matplotlib interactively:		Or, if you want to use matplotlib interactively:
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	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:		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~~>		<syntaxhighlight lang=nix>pythonDebug = pkgs.python310.override { enableDebug = true; };</syntaxhighlight>

	== Installing Multiple Versions ==		== Installing Multiple Versions ==
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	=== Regression ===		=== Regression ===
	With the <code>nixpkgs</code> version of Python you can expect anywhere from a 30-40% regression on synthetic benchmarks. For example:		With the <code>nixpkgs</code> version of Python you can expect anywhere from a 30-40% regression on synthetic benchmarks. For example:
	<syntaxhighlight lang=~~python~~>## Ubuntu's Python 3.8		<syntaxhighlight lang=console>## Ubuntu's Python 3.8
	username:dir$ python3.8 -c "import timeit; print(timeit.Timer('for i in range(100): oct(i)', 'gc.enable()').repeat(5))"		username:dir$ python3.8 -c "import timeit; print(timeit.Timer('for i in range(100): oct(i)', 'gc.enable()').repeat(5))"
	[7.831622750498354, 7.82998560462147, 7.830805554986, 7.823807033710182, 7.84282516874373]		[7.831622750498354, 7.82998560462147, 7.830805554986, 7.823807033710182, 7.84282516874373]
Line 715:		Line 719:
	=== My module cannot be imported ===		=== My module cannot be imported ===

	If you are unable to do `import yourmodule` there are a number of reasons that could explain that.		If you are unable to do <code>import yourmodule</code> there are a number of reasons that could explain that.

	First, make sure that you installed/added your module to python. Typically you would use something like <code> (python3.withPackages (ps: with ps; [ yourmodule ]))</code> in the list of installed applications.		First, make sure that you installed/added your module to python. Typically you would use something like <code> (python3.withPackages (ps: with ps; [ yourmodule ]))</code> in the list of installed applications.
Line 721:		Line 725:
	It is also still possible (e.g. when using nix-shell) that you aren't using the python interpreter you want because another package provides its own <code>python3.withPackages</code> in buildInputs, for example, yosys. In this case, you should either include that package (or all needed packages) in your withPackages list to only have a single Python interpreter. Or you can change the order of your packages, such that the <code>python3.withPackages</code> comes first, and becomes the Python interpreter that you get.		It is also still possible (e.g. when using nix-shell) that you aren't using the python interpreter you want because another package provides its own <code>python3.withPackages</code> in buildInputs, for example, yosys. In this case, you should either include that package (or all needed packages) in your withPackages list to only have a single Python interpreter. Or you can change the order of your packages, such that the <code>python3.withPackages</code> comes first, and becomes the Python interpreter that you get.

	If you packaged yourself your application, make sure to use <code>buildPythonPackage</code> and not <code>buildPythonApplication</code> or <code>stdenv.mkDerivation</code>. The reason is that <code>python3.withPackages</code> [https://github.com/NixOS/nixpkgs/blob/91d1eb9f2a9c4e3c9d68a59f6c0cada8c63d5340/pkgs/top-level/python-packages.nix#L57 filters] the packages to check that they are built using the appropriate python interpreter: this is done by verifying that the derivation has a <code>pythonModule</code> attribute and only buildPythonPackage [https://github.com/NixOS/nixpkgs/blob/91d1eb9f2a9c4e3c9d68a59f6c0cada8c63d5340/pkgs/top-level/python-packages.nix#L43 sets this value] (passthru [https://github.com/NixOS/nixpkgs/blob/91d1eb9f2a9c4e3c9d68a59f6c0cada8c63d5340/pkgs/top-level/python-packages.nix#L75 here]) thanks to, notably <code>passthru = { pythonModule = python; }</code>. If you used <code>stdenv.mkDerivation</code> then you can maybe set this value manually, but it's safer to simply use <code>buildPythonPackage {format = "other"; … your derivation …}</code> instead of <code>mkDerivation</code>.		If you packaged yourself your application, make sure to use <code>buildPythonPackage</code> and <b>not</b> <code>buildPythonApplication</code> or <code>stdenv.mkDerivation</code>. The reason is that <code>python3.withPackages</code> [https://github.com/NixOS/nixpkgs/blob/91d1eb9f2a9c4e3c9d68a59f6c0cada8c63d5340/pkgs/top-level/python-packages.nix#L57 filters] the packages to check that they are built using the appropriate python interpreter: this is done by verifying that the derivation has a <code>pythonModule</code> attribute and only buildPythonPackage [https://github.com/NixOS/nixpkgs/blob/91d1eb9f2a9c4e3c9d68a59f6c0cada8c63d5340/pkgs/top-level/python-packages.nix#L43 sets this value] (passthru [https://github.com/NixOS/nixpkgs/blob/91d1eb9f2a9c4e3c9d68a59f6c0cada8c63d5340/pkgs/top-level/python-packages.nix#L75 here]) thanks to, notably <code>passthru = { pythonModule = python; }</code>. If you used <code>stdenv.mkDerivation</code> then you can maybe set this value manually, but it's safer to simply use <code>buildPythonPackage {format = "other"; … your derivation …}</code> instead of <code>mkDerivation</code>.

	== See also ==		== See also ==

Turnipjs: update line numbers referring to snippet

2026-02-12T21:09:28Z

update line numbers referring to snippet

← Older revision		Revision as of 21:09, 12 February 2026
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	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>.

IllustratedMan-code: Adds a section about using rPackages with rpy2 in python

2025-11-13T16:16:18Z

Adds a section about using rPackages with rpy2 in python

@@ Line 39: / Line 39: @@
    ]))
 ];
 </syntaxhighlight>

Aktaboot: fix broken link to pyproject docs

2025-10-18T15:44:23Z

fix broken link to pyproject docs

← Older revision		Revision as of 15:44, 18 October 2025
Line 546:		Line 546:
	[project.scripts]		[project.scripts]
	cli = "app.main:main"		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://nix~~-community~~.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">		</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";		description = "A basic flake using pyproject.toml project metadata";

Lukeb: fixed broken link for pyproject use-cases

2025-08-12T18:59:19Z

fixed broken link for pyproject use-cases

← Older revision		Revision as of 18:59, 12 August 2025
Line 531:		Line 531:
	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"

LovesTha: /* Using buildFHSEnv */ as second recommended option

2025-07-18T01:42:51Z

Using buildFHSEnv: as second recommended option

← Older revision		Revision as of 01:42, 18 July 2025
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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