Simple how-to for poetry2nix
This is also explained on https://www.tweag.io/blog/2020-08-12-poetry2nix/
See also https://github.com/nix-community/poetry2nix
Why?
This was good exercise in learning how to use poetry2nix. This can serve as an introduction/stencil for other projects.
How?
poetry is Nix-agnostic, but poetry is much more reproducible than pip. This makes poetry very attractive from Nix's perspective; to the point where a Nix expression can be written (poetry2nix) which reads in poetry-related files, and can generate Nix derivations from these. With such Nix derivations:
- We natively fetch from PyPI - same repo pip uses.
- We natively install to /nix/store - like any native Nix package. And thus enjoy nix's benefits; shared sparse install, gc, etc.
- We avoid shellHook always running venv+pip.
- We avoid placing venv in some humanly-decided rando location.
Example 1: Update the lockfile
eisbaw@t460s:~/topics/poetry_nix_demo2$ time nix-shell --pure --run "exit 0"
Yay poetry.lock exists. I'll honor it
You have a perfectly usable environment now :)
real 0m1.435s
user 0m1.234s
sys 0m0.200s
eisbaw@t460s:~/topics/poetry_nix_demo2$ rm poetry.lock
eisbaw@t460s:~/topics/poetry_nix_demo2$ time nix-shell --pure --run "exit 0"
Boo! You don't have a lock file - so I'll make it now
Updating dependencies
Resolving dependencies... (0.2s)
Writing lock file
Lockfile created. But this nix-shell is unusable; start it again. Exiting for now.
real 0m2.451s
user 0m2.221s
sys 0m0.165s
eisbaw@t460s:~/topics/poetry_nix_demo2$ time nix-shell --pure --run "exit 0"
Yay poetry.lock exists. I'll honor it
You have a perfectly usable environment now :)
real 0m1.425s
user 0m1.191s
sys 0m0.234s
eisbaw@t460s:~/topics/poetry_nix_demo2$ ls poetry.lock
poetry.lock
Example 2: Usage
$PYTHONPATH should be updated thanks to poetry2nix, so the dependencies specified in the poetry.lock (and thus pyproject.toml) should be present:
nix-shell --pure --run "python3 -c 'import imgapp; print(imgapp)'"