Select pyenv environment based on folder .python-version file

[dan-blanchard]

Environment data

• VS Code version: 1.21.1
• Extension version (available under the Extensions sidebar): 2018.2.1
• OS and version: macOS 10.13.3
• Python version (& distribution if applicable, e.g. Anaconda): Python 3.6.4
• Type of virtual environment used (N/A | venv | virtualenv | conda | ...): pyenv
• Relevant/affected Python packages and their versions: pyenv 1.2.1

Actual behavior

You have to manually select the pyenv interpreter for each workspace folder.

Expected behavior

It should detect the workspace pyenv interpreter based on the .python-version file present in the workspace folder root.

For example, every folder I have added to my workspace has a .python-version file that pyenv creates when you run pyenv local NAME_OF_VENV in that folder. The file contains a single string which is the name of the folder/symlink in ~/.pyenv/versions/ that should be used.

[brettcannon]

https://github.com/pyenv/pyenv#choosing-the-python-version has the specification on how pyenv chooses an interpreter by default. I think detecting the file and using it as appropriate seems like a sensible enhancement (maybe even the file traversal to the parent directory, but not as sure on that one).

[neverfox]

@brettcannon I'm not sure if it's possible but you should be able to let pyenv do the heavy lifting if you use the shims it provides as the interpreter, as long as its run in a context (i.e. directory) aware way.

[eugenweissbart]

Hi @brettcannon, will this issue be addressed in any near future? Thanks!

[brettcannon]

@eugenweissbart sorry, we don't give ETAs since they always turn out to be wrong. 😉

[djdembeck]

Would like to see this feature as well.

[brettcannon]

@djdembeck please make sure to upvote the opening comment as that's how we determine community interest.

[karrtikr]

Spike results

Couple ways to go about it:

1. pyenv determines which Python version to use by reading it from the following sources, in this order: https://github.com/pyenv/pyenv/blob/master/README.md#understanding-python-version-selection

   Pros: No need to launch the pyenv binary

   Cons: This would imply that we do the heavy lifting:

   • Looking into parent directories
   • Reading and parsing .python-version file correctly
   • Keeping up to date with the doc to make sure the order isn't changing

2. Run <pyenv> which python in the cwd of the workspace. We can either:
   2.1 Locate the pyenv binary and run the command using child_process.exec.

   For eg. it could be /home/node/.pyenv/bin/pyenv which python.

   2.2 Open a hidden terminal and simply run the command: pyenv which python.

   2.2 is potentially more reliable as it makes sure shell initialization scripts are being run, which include pyenv install instructions. However this requires onDidExecuteTerminalCommand does not fire events for hidden terminal vscode#199611 to be fixed.

To avoid relying on internal details of pyenv and keep things simple, approach 2 sounds reasonable.

Tested 2.1 and it seems to be working just fine on Windows and Linux, despite not executing the shell instructions, hence deciding to go with that for now. If we observe issues with that, we can switch to 2.2 once microsoft/vscode#199611 is fixed.

[karrtikr]

Fix should be out in the pre-release version of the extension, use the following to try it out: