pythonPackages.venvShellHook: init

This is a hook that loads a virtualenv from the specified `venvDir`
location. If the virtualenv does not exist, it is created.

doc/languages-frameworks/python.section.md

···
 - `pythonRemoveBinBytecode` to remove bytecode from the `/bin` folder.
 - `setuptoolsBuildHook` to build a wheel using `setuptools`.
 - `setuptoolsCheckHook` to run tests with `python setup.py test`.
+- `venvShellHook` to source a Python 3 `venv` at the `venvDir` location. A `venv` is created if it does not yet exist.
 - `wheelUnpackHook` to move a wheel to the correct folder so it can be installed with the `pipInstallHook`.
 
 ### Development mode

pkgs/development/interpreters/python/hooks/default.nix

···
 { python
 , callPackage
 , makeSetupHook
+, disabledIf
+, isPy3k
+, ensureNewerSourcesForZipFilesHook
 }:
 
 let
···
         inherit pythonCheckInterpreter setuppy;
       };
     } ./setuptools-check-hook.sh) {};
+
+  venvShellHook = disabledIf (!isPy3k) (callPackage ({ }:
+    makeSetupHook {
+      name = "venv-shell-hook";
+      deps = [ ensureNewerSourcesForZipFilesHook ];
+      substitutions = {
+        inherit pythonInterpreter;
+    };
+  } ./venv-shell-hook.sh) {});
 
   wheelUnpackHook = callPackage ({ wheel }:
     makeSetupHook {

pkgs/development/interpreters/python/hooks/venv-shell-hook.sh

···
+venvShellHook() {
+    echo "Executing venvHook"
+    runHook preShellHook
+
+    if [ -d "${venvDir}" ]; then
+      echo "Skipping venv creation, '${venvDir}' already exists"
+    else
+      echo "Creating new venv environment in path: '${venvDir}'"
+      @pythonInterpreter@ -m venv "${venvDir}"
+    fi
+
+    source "${venvDir}/bin/activate"
+
+    runHook postShellHook
+    echo "Finished executing venvShellHook"
+}
+
+if [ -z "${dontUseVenvShellHook:-}" ] && [ -z "${shellHook-}" ]; then
+    echo "Using venvShellHook"
+    if [ -z "${venvDir-}" ]; then
+        echo "Error: \`venvDir\` should be set when using \`venvShellHook\`."
+        exit 1
+    else
+        shellHook=venvShellHook
+    fi
+fi

pkgs/top-level/python-packages.nix

···
   inherit buildSetupcfg;
 
   inherit (callPackage ../development/interpreters/python/hooks { })
-    eggUnpackHook eggBuildHook eggInstallHook flitBuildHook pipBuildHook pipInstallHook pytestCheckHook pythonCatchConflictsHook pythonImportsCheckHook pythonRemoveBinBytecodeHook setuptoolsBuildHook setuptoolsCheckHook wheelUnpackHook;
+    eggUnpackHook eggBuildHook eggInstallHook flitBuildHook pipBuildHook pipInstallHook pytestCheckHook pythonCatchConflictsHook pythonImportsCheckHook pythonRemoveBinBytecodeHook setuptoolsBuildHook setuptoolsCheckHook venvShellHook wheelUnpackHook;
 
   # helpers