Better python dev experience with direnv + nix + pipenv

envrc.bash

use nix

layout_nix_pipenv() {

  if [[ ! -f Pipfile ]]; then
    log_error 'No Pipfile found.  Use `pipenv` to create a Pipfile first.'
    exit 2
  fi

  # Use ram as virtualenv storage
  local tmpdir
  case $(uname -s) in
    Linux*) tmpdir=$XDG_RUNTIME_DIR;;
    Darwin*) tmpdir_SDK=$TMPDIR;;
    *) tmpdir=/tmp
  esac
  if test "$tmpdir" = ""; then
      tmpdir="/tmp"
  fi

  # Create a directory to hold all virtual envs
  # We dont want $tmpdir to be too messy
  local venv_base=$tmpdir/direnv-venvs
  mkdir -p $venv_base

  # Use nix-instantiate to figure out all the inputs for this env
  # This makes sure that the virtual env has consistent dynamic linking
  local env_hash=$(nix-instantiate ./shell.nix 2> /dev/null | shasum -a 256 | cut -d ' ' -f 1 | cut -c-7)
  local venv_dir=$venv_base/$(basename $(pwd))-$env_hash

  local venv_exists=1
  local VENV=$venv_dir
  if [[ -z $VENV || ! -d $VENV ]]; then
    venv_exists=0
    python -m venv $VENV
  fi
  source $VENV/bin/activate

  if [ $venv_exists -eq 0 ]; then
      pipenv install --dev
  fi

  export VIRTUAL_ENV=$(pipenv --venv)
  PATH_add "$VIRTUAL_ENV/bin"

  # Work around issue https://github.com/NixOS/nixpkgs/issues/39558
  export PYTHONPATH=$(pipenv --venv)/lib/python*/site-packages/:$PYTHONPATH

}

layout_nix_pipenv