pypi2nix
is a command line tool that generates Nix expressions from different requirements.txt
. This is useful for:
- Building a Nix derivation for a program written in Python as part of packaging it.
Setting up a development environment to hack on a program written in Python.
The only way we can fix bugs with pypi2nix is if you report them. Please create an issue if you discover problems.
pypi2nix
will (until further notice) only work with latest unstable channel. This is due to ongoing changes in Python infrastructure happening in Nixpkgs.
The Nixpkgs manual section about Python makes good reading if you haven't seen it already.
Make sure Nix is installed:
% curl https://nixos.org/nix/install | sh
And now install it using nix-env command:
% nix-env -if https://github.com/nix-community/pypi2nix/tarball/master
Your system needs to have nix
installed on it. Currently pypi2nix
is only tested against linux
systems. Supported nixpkgs
channels are nixos-19.09
and nixos-unstable
. Due to the nature of nixos-unstable
the occasional breakage of pypi2nix
is to be expected. We try to provide fixes in that regard in a timely manner.
The easiest way to generate a Nix expressions is to invoke:
% pypi2nix -e packageA -e packageB==0.1
If you also have a requirements.txt
file for your Python project you can use the -r
option.
% pypi2nix -e packageA -e packageB==0.1 \
-r requirements.txt -r requirements-dev.txt
Option -V
tells pypi2nix which python version to be used. To see which Python versions are available consult pypi2nix --help
.
Once Nix expressions are generated you should be able to see 3 new files:
requirements_frozen.txt
- full frozen set for your for your pypi2nix call. This is the output you would expect frompip freeze
.requirements.nix
is a file which contains a nix expression to for the package set that was built.requirements_override.nix
- this is an empty file which lets you override generated nix expressions.
Build one package:
% nix build -f requirements.nix packages.empy
Build all packages:
% nix build -f requirements.nix packages
Build python interpreter with all packages loaded:
% nix build -f requirements.nix interpreter
% ./result/bin/python -c "import empy"
Enter development environment:
% nix run -f requirements.nix interpreter
[user@localhost:~/dev/nixos/pypi2nix) % python -c "import empy"
If you are working on a project where its dependencies are defined in requirements.txt
then you can create a default.nix
and add generated packages as buildInputs
, as demonstrated here:
{}:
let
python = import ./requirements.nix { inherit pkgs; };
in python.mkDerivation {
name = "ProjectA-1.0.0";
src = ./.;
buildInputs = [
python.packages."coverage"
python.packages."flake8"
python.packages."mock"
python.packages."pytest"
python.packages."pytest-asyncio"
python.packages."pytest-cov"
python.packages."pytest-mock"
python.packages."pytest-xdist"
python.packages."virtualenv"
];
propagatedBuildInputs = [
python.packages."aiohttp"
python.packages."arrow"
python.packages."defusedxml"
python.packages."frozendict"
python.packages."jsonschema"
python.packages."taskcluster"
python.packages."virtualenv"
];
...
}
As you can see you can access all packages via python.packages."<name>"
. If you want to depend on all packages you can even do:
propagatedBuildInputs = builtins.attrValues python.packages;
-v
Increase amount and detail of information output to the user. Verbosity levels are
ERROR
,WARNING
,INFO
andDEBUG
in that order. The default verbosity isINFO
.-q
Reduce amount and detail of information output to the user. See
-v
for more information.-I/--nix-path TEXT
Add entries to the
NIX_PATH
environment variable similarly to how-I
works withnix
executables likenix-build
. This can be useful for generating package sets based on a differentnixpkgs
version than the one used one the local system.--nix-shell PATH
Path to an alternative version of the
nix-shell
command. The default is the first executable that will be found in the currentPATH
of the system.--version
Show the current version of
pypi2nix
--basename TEXT
This option determins the name the produced files. So with
--basename environment
you would get the filesenvironment.nix
,environment_frozen.nix
andenvironment_override.nix
.--extra-build-inputs/-E TEXT
Extra build inputs that the required python packages need to run, e.g.
libffi
orlibgl
. In that case you would provide-E "libffi libgl"
. These nix packages will be available in the build environment for the wheels.--emit-extra-build-inputs/--no-emit-extra-build-inputs
These options let you control if external build dependencies specified via
-E
will end up in the generated nix package set. Please note that if you select this option, your overrides need to make sure that python packages find their respective external dependencies.--extra-env/-N TEXT
Extra environment variables that will be passed to the build environment. Note that you can use nix expressions in this string, e.g.
-N 'BERKELEYDB_DIR=${pkgs.db.dev}'
.--enable-tests/-T
Specify this flag if you want to enable the check phase of all packages in the generated nix expression. Please note that this feature is highly exprimental and will probably not work for your use case.
--python-version/-V
Specify the python version you want the requirement set to be built with. The default is
3
which translates to thepython3
derivation ofnixpkgs
.--requirements/-r FILE
Specify a requirements file, similar as you would with
pip
.pypi2nix
tries to be fully compatible with the file format ofpip
.--editable/-e TEXT
This option allows you to specify individual requirements that get added to the requirement set, e.g.
pypi2nix -e attrs
,pypi2nix -e $HOME/src/myproject#egg=myproject
orpypi2nix -e .#egg=myegg
.--setup-requires/-s TEXT
Allows you to specify python packages that need to be present in the build environment of other packages, a good example of this would be
setuptools-scm
. Note thatpypi2nix
tries to detect these dependencies on its own. You only need to specify this flag in cases where a package author or maintainer forgot to mention build time dependencies in their setup or neithersetup.cfg
norpyproject.toml
is used.--overrides/-O URL
Allows you to specify additional overrides that conform to the general structure of
requirements_override.nix
. We support regular URLs withhttp
andhttps
scheme and alsogit
. An example for usinghttps
would bepypi2nix -O https://myoverrides.test/overrides.nix
. Reusing an overlay from a git repository would be done like so:pypi2nix -O git+https://github.com/nix-community/pypi2nix.git&path=requirement_override.nix
. Please keep in mind that these overrides are incorporated in a nix expression with a precalculated hash value. So if the file changes upstream your generated package can not be built anymore.--default-overrides/--no-default-overrides
Pull in overrides from
https://github.com/nix-community/pypi2nix-overrides
. This feature is enabled by default.--wheels-cache/-W TEXT
A location where prebuilt wheels can be found. This option will ultimately be passed to
pip --find-links
. Only point to wheels that are built throughpypi2nix
on your own or a very similar system.--build-directory TEXT
Warning A bug in
pypi2nix
currently prevents some packages from being built with this option set. It is recommended to not use this flag.The directory where pypi2nix would build the python environment to generate the desired nix expression. If not specified, the build directory will be temporary and is deleted before the program exits.
I hope nobody is expecting pypi2nix
to do always a perfect job. In Python packaging, there are just too many different cases that we will never be able to cover. What pypi2nix
tries to do is to get you very close.
Sometimes pypi2nix
fails entirely. If this happens, open a bug --it's almost always a bug in pypi2nix
. However, sometimes pypi2nix
succeeds but the resulting requirements.nix
file fails during the building of your Python package. Depending on what the problem is, this section may be helpful.
Quite a few Python packages require non-Python dependencies to be present at build time. These packages will fail to build with error messages about not being able to find foo.h
or some fooconfig
file. To work around this, pypi2nix
has -E
options which can be used to include extra non-Python dependencies.
For example, psycopg2
requires pg_config
binary to be present at installation time:
% pypi2nix -v -V 2.7 -e psycopg2 -E postgresql
lxml
requires libxml2
and libxslt
system package:
% pypi2nix -v -V 2.7 -e lxml -E libxml2 -E libxslt
Some packages expect additional environment variables to be set:
% pypi2nix -v -V 2.7 -e bsddb3 -N 'BERKELEYDB_DIR=${pkgs.db.dev}'
Some other failures might be caused because the derivation that pypi2nix
wrote was incomplete. A very common situation is that pypi2nix
didn't include all the dependencies of some package. As an example, execnet
depends on setuptools-scm
, but pypi2nix
may not detect this.
When this happens, Nix will fail to build execnet
, perhaps with an error message from distutils/setuptools complaining that it can't find a distribution for setuptools-scm
. What's happening here is that normally execnet
would fetch setuptools-scm
from PyPI, but Nix disables network access to guarantee reproducability. So when you build execnet
, it fails to find setuptools-scm
.
For these situations, pypi2nix
provides a requirements_override.nix
file, which lets you override anything that it generated. You can even add new packages to the dependency set this way.
As an example, let's add setuptools-scm
as a build-time dependency of execnet
. Here's the requirements_override.nix
:
{ pkgs, python }:
self: super: {
"execnet" = python.overrideDerivation super."execnet" (old: {
buildInputs = old.buildInputs ++ [ self."setuptools-scm" ];
});
}
In a similar way, you can add or remove any Python package.
In addition to the empty autogenerated requirements_overrides.nix
file, you can include pre-existing overrides files. These overrides will be included the same way as your requirements_overrides.nix
.
The pypi2nix
author also maintains a set of "default" overrides at https://github.com/nix-community/pypi2nix-overrides/blob/master/overrides.nix --you can include these by using the --default-overrides
argument to pypi2nix
. These overrides are designed in such a way that they only override dependencies that were already present in your requirements.nix
.
You can also include an overrides file using the -O
command line argument. pypi2nix
can fetch these overrides from a local file or over certain common protocols.
http
andhttps
pypi2nix -V 3 --overrides https://raw.githubusercontent.com/nix-community/pypi2nix-overrides/master/overrides.nix
Note that the generated Nix expression will check if contents of the overrides file differs from when the Nix expression was built, and fail if this was the case (or the file does not exist anymore).
- Local files
pypi2nix -V 3 --override ../some/relative/path --override /some/absolute/path
- Git repositories
pypi2nix -V 3 --override git+https://github.com/nix-community/pypi2nix.git#path=overrides.nix
If you want to import a file from a specific git repository you have to prefix its URL with
git+
, quite similar to how you would do in arequirements.txt
file forpip
.
Nothing speaks better than an example:
{ }:
let
pkgs = import <nixpkgs> {};
python = import ./requirements.nix { inherit pkgs; };
in python.mkDerivation {
name = "projectA-1.0.0";
src = ./.;
buildInputs = [
python.packages."coverage"
python.packages."flake8"
python.packages."mock"
python.packages."pytest"
python.packages."pytest-asyncio"
python.packages."pytest-cov"
python.packages."pytest-mock"
python.packages."pytest-xdist"
];
propagatedBuildInputs = [
python.packages."aiohttp"
python.packages."arrow"
python.packages."defusedxml"
python.packages."frozendict"
python.packages."jsonschema"
];
checkPhase = ''
export NO_TESTS_OVER_WIRE=1
export PYTHONDONTWRITEBYTECODE=1
flake8 src/
py.test --cov=src -cov-report term-missing
coverage html
'';
}
Important to know here is that you instantiate all generated packages as python = import ./requirements.nix { inherit pkgs; };
which gives you a Python environment with all the packages generated by pypi2nix
as well as some common utilities.
To create a package you use python.mkDerivation
which works like the pythonPackages.buildPythonPackage
function in nixpkgs
. All generated packages are available as one attribute set under python.packages
.
One of future goals of pypi2nix
project is to also improve the UX of our Python tooling in nixpkgs. While this is very hard to do within nixpkgs
it is almost trivial to experiment with this outside nixpkgs
.
A working example is worth 1000 words.
overlay.nix:
self: super:
{
customPython =
(import ./requirements.nix { pkgs = self; });
}
shell.nix:
with (import <nixpkgs> { overlays = [ (import ./overlay.nix) ]; });
customPython.interpreter
Clone pypi2nix repository and using nix-shell
command enter development environment.:
% git clone https://github.com/nix-community/pypi2nix
% cd pypi2nix
% nix-shell
Code is located in src/pypi2nix
.
Pypi2nix comes with two kinds of tests: unit tests and integration tests. They can be found in the folders /unittests
and /integrationtests
respectively.
Unit tests are straight forward. They are run via pytest and (try to) follow pytest best practices. Idealy all of pypi2nix's code should be covered by unittests. If possible unittests should not go online and fetch data from the internet. If this cannot be avoided use the @nix
decorator, found in unittests.switches
to mark tests that require network access.
Integration tests are a little bit more involved. We implemented a small framework to write new tests and maintain old ones. Check out integrationtests.framework
for information on how to write custom integration tests. To run all integration tests run run_integration_tests.py
from the scripts
directory. If you use nix-shell
to create your development environment then the scripts
directory should be in you PATH
variable.
Please note that all integration test cases are classes deriving from integrationtests.framework.IntegrationTest
. Also all these tests must end with TestCase
, e.g. MyCustomTestCase
.
The scripts
folder contains programs that help to maintain the repository. We expect the user to have all the packages from the build environment of pypi2nix installed. We register the scripts
directory in the users PATH
if they choose to enter nix-shell
in the top level directory of this project.