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https://github.com/dtgoitia/nix-python
Minimal Python environment set up using nix flakes.
https://github.com/dtgoitia/nix-python
nix python
Last synced: 2 months ago
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Minimal Python environment set up using nix flakes.
- Host: GitHub
- URL: https://github.com/dtgoitia/nix-python
- Owner: dtgoitia
- Created: 2024-08-21T07:46:43.000Z (5 months ago)
- Default Branch: main
- Last Pushed: 2024-08-21T09:51:39.000Z (5 months ago)
- Last Synced: 2024-10-10T23:22:01.610Z (3 months ago)
- Topics: nix, python
- Language: Nix
- Homepage:
- Size: 2.93 KB
- Stars: 2
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
# Python development environment with nix
## What is this?
The bare minimum code needed to set up a Python environment using [nix flakes][2].
In this setup, the Python packages are not installed using [nix][1]. Instead, nix is only used to build the desired Python version, then this Python version is used to create a virtual environment, and inside the virtual environment you are free to install whatever you whish using `pip`.
In this case, nix is effectively replacing [pyenv][3], with the benefit that you could include non-Python packages (e.g.: `jq`) and pin their versions.
### Why not install Python packages directly with nix?
nix is capable of [directly installing Python packages][4] as well. However, at this point in my nix journey, I find the process too rigid for my taste.
## Usage
```shell
nix develop
python -m venv .venv
. .venv/bin/activate
pip install -r requirements.txt
```
### For the curious
#### What do the above instructions do?
The first line spawns a [nix shell][5]:
```shell
nix develop
```
The first time it takes a bit (~7min) to build. Bear in mind that this step is build your desired Python version from source. After the first run, the build is cached, so it takes ~1s to load.
At this point you are inside a nix shell, and the desired Python version should be available to you:
```shell
which python
# /nix/store/sxazgaidqcw9gzarla17qka6071vwgv0-python3-3.10.1-env/bin/python
python -V
# Python 3.10.1
```
You could be now tempted to use `pip` to install Python packages - after all, we have Python installed, right? Not quite. Try to find the version of `pip`:
```shell
pip -V
```
You will either (a) get an error saying `pip` command is not found, or (b) you had `pip` installed system-wide (outside this nix flake, that is). Use `which pip` to confirm.
Regardless of you observing (a) or (b), if you haven't modified `flake.nix`, `pip` should not have been installed with the nix flake alongside the Python you chose. This is desired. Why? You won't be able to install packages as usual if you install `pip` using the nix flake. See [_Can I install pip via nix flake?_](#can-i-install-pip-via-nix-flake) for a more detailed explanation.
How can you install Python packages then? From within the nix shell, create a Python virtual environment, and follow your preferred way of installing dependencies inside this Python virtual environment:
```shell
python -m venv .venv
. .venv/bin/activate
pip install -r requirements.txt
```
#### Can I install `pip` via nix flake?
Let's give it a go and see what happens, shall we?
1. Make sure you are not in any previous nix shell.
2. Edit `flake.nix` to include `pip` as a nix package of the `myPython` nix package.
```diff
pkgs = import nixpkgs { inherit system; };
myPython = nixpkgs-python.packages.${system}.${pythonVersion};
+ myPythonWithPackages = myPython.withPackages (ps: with ps; [
+ pip
+ ]);
in
{
devShells.${system}.default = pkgs.mkShell {
buildInputs = [
- myPython
+ myPythonWithPackages
];
shellHook = ''
```
3. Rebuild and jump into the shell:
```shell
nix develop
```
4. Confirm `pip` is installed via nix shell - must have the `/nix/store` prefix below with a different hash:
```shell
which pip
# /nix/store/sxazgaidqcw9gzarla17qka6071vwgv0-python3-3.10.1-env/bin/pip
```
5. Install any Python package using the `pip` installed via nix flake:
```shell
pip install ipdb
# Collecting ipdb
# (...)
# ERROR: Could not install packages due to an OSError: [Errno 13] Permission denied: '/nix/store/sxazgaidqcw9gzarla17qka6071vwgv0-python3-3.10.1-env/lib/python3.10/site-packages/wcwidth'
# Check the permissions.
```
Ta-da! 🎉 In the nix world, you are not supposed to use `pip` directly to install Python packages. Instead, you wrap those Python packages to convert nix packages, and you install those wrapped nix packages. See [docs][4].
## Acknowledgement
Thank you [`nixpkgs-python`][6] for making it so accessible.
[1]: https://nix.dev/ "nix"
[2]: https://nix.dev/concepts/flakes.html "nix | flakes"
[3]: https://github.com/pyenv/pyenv "pyenv"
[4]: https://nixos.wiki/index.php?title=Python#Installation "NixOS Wiki | Python | Installation"
[5]: https://nix.dev/tutorials/first-steps/declarative-shell.html "nix | shell"
[6]: https://github.com/cachix/nixpkgs-python "nixpkgs-python"