diff options
author | Dima <dgoldin+github@protonmail.ch> | 2020-01-12 18:27:17 +0100 |
---|---|---|
committer | Jon <jonringer@users.noreply.github.com> | 2020-01-20 18:01:12 -0800 |
commit | 25d0d2b5e88071f09d701c1ad3958796a62e3c9d (patch) | |
tree | 39ce87591ef49e01b5777955eddf7f53ffcd6b38 /doc | |
parent | ff708504cd2fa33a1b042ebd9da78187411ac66d (diff) |
doc: python: refreshing virtualenv section for venv
Updating section about imperative use of ad-hoc virtual-environments for
use of pythons built-in `venv` module via venvShellHook. Also trying to
make it a bit friendlier to beginners by adding a bit more explanation
to the code snippet and some remarks old-school virtualenv.
Adjusting for venvShellHook and adding manual example
Adding pip install and replacing python2 example with python3
Diffstat (limited to 'doc')
-rw-r--r-- | doc/languages-frameworks/python.section.md | 77 |
1 files changed, 60 insertions, 17 deletions
diff --git a/doc/languages-frameworks/python.section.md b/doc/languages-frameworks/python.section.md index bbcf82f7ed69..9b6de47c8e86 100644 --- a/doc/languages-frameworks/python.section.md +++ b/doc/languages-frameworks/python.section.md @@ -1029,36 +1029,43 @@ If you want to create a Python environment for development, then the recommended method is to use `nix-shell`, either with or without the `python.buildEnv` function. -### How to consume python modules using pip in a virtualenv like I am used to on other Operating Systems ? +### How to consume python modules using pip in a virtual environment like I am used to on other Operating Systems? -This is an example of a `default.nix` for a `nix-shell`, which allows to consume a `virtualenv` environment, +While this approach is not very idiomatic from Nix perspective, it can still be useful when dealing with pre-existing +projects or in situations where it's not feasible or desired to write derivations for all required dependencies. + +This is an example of a `default.nix` for a `nix-shell`, which allows to consume a virtual environment created by `venv`, and install python modules through `pip` the traditional way. Create this `default.nix` file, together with a `requirements.txt` and simply execute `nix-shell`. ```nix -with import <nixpkgs> {}; +with import <nixpkgs> { }; let - pythonPackages = python27Packages; -in - -stdenv.mkDerivation { + pythonPackages = python3Packages; +in pkgs.mkShell rec { name = "impurePythonEnv"; + venvDir = "./.venv"; + buildInputs = [ + # A python interpreter including the 'venv' module is required to bootstrap + # the environment. + pythonPackages.python - src = null; + # This execute some shell code to initialize a venv in $venvDir before + # dropping into the shell + pythonPackages.venvShellHook + + # Those are dependencies that we would like to use from nixpkgs, which will + # add them to PYTHONPATH and thus make them accessible from within the venv. + pythonPackages.numpy + pythonPackages.requests - buildInputs = [ - # these packages are required for virtualenv and pip to work: - # - pythonPackages.virtualenv - pythonPackages.pip # the following packages are related to the dependencies of your python # project. # In this particular example the python modules listed in the # requirements.txt require the following packages to be installed locally # in order to compile any binary extensions they may require. - # taglib openssl git @@ -1068,11 +1075,47 @@ stdenv.mkDerivation { zlib ]; + # Now we can execute any commands within the virtual environment + postShellHook = '' + pip install -r requirements.txt + ''; + +} +``` + +In case the supplied venvShellHook is insufficient, or when python 2 support is needed, +you can define your own shell hook and adapt to your needs like in the following example: + +```nix +with import <nixpkgs> { }; + +let + venvDir = "./.venv"; +in pkgs.mkShell rec { + name = "impurePythonEnv"; + buildInputs = [ + python3Packages.python + python3Packages.virtualenv + ... + ]; + + # This is very close to how venvShellHook is implemented, but + # adapted to use 'virtualenv' shellHook = '' - # set SOURCE_DATE_EPOCH so that we can use python wheels SOURCE_DATE_EPOCH=$(date +%s) - virtualenv --python=${pythonPackages.python.interpreter} --no-setuptools venv - export PATH=$PWD/venv/bin:$PATH + + if [ -d "${venvDir}" ]; then + echo "Skipping venv creation, '${venvDir}' already exists" + else + echo "Creating new venv environment in path: '${venvDir}'" + ${pythonPackages.python.interpreter} -m venv "${venvDir}" + fi + + # Under some circumstances it might be necessary to add your virtual + # environment to PYTHONPATH, which you can do here too; + # PYTHONPATH=$PWD/${venvDir}/${python.sitePackages}/:$PYTHONPATH + + source "${venvDir}/bin/activate" pip install -r requirements.txt ''; } |