Emacs for Python and Poetry Using `basedpyright-langserver`

I am very pleased with my current emacs setup for Python, but I found setup to be a little tricky. I will document my setup here for my future self and for any other Pythonistas looking for a solid emacs config.

Why basedpyright?

Up to this point, I've been using mypy --strict on the command line for all my typechecking needs, but mypy is quite slow even for very small codebases, and even in --strict mode it is just not as strict as it could be. It's also not a language server, which I want for my emacs setup.

basedpyright is a fork of pyright with some excellent improvements in both checking and in reliability. It is a fast and wonderfully strict typechecker with some good linting capabilities additionally.

The only drawbacks I am experiencing are that it doesn't play quite as nicely as mypy with the boto3-stubs clients for AWS and that it uses nonstandard # pyright: ignore comments instead of the standard # type: ignore comments, but I can live with those issues in favor of a rigorously strict type-checking experience.

Configuring your Poetry projects to work with basedpyright or pyright

If you have existing projects that use Poetry, you're going to want to fiddle a little with your virtual environment.

Go to the root of each of your projects and run the following command:

poetry config --local virtualenvs.in-project true

This will create a poetry.toml file if one does not already exist and add a corresponding setting.

This, however, will not actually move your existing virtual environment. In order for this change to take effect, you have to remove your existing virtual environment, which you can find by running

poetry env info --path

Don't forget to add the .venv path to your .gitignore and the configuration for any other tools you might use, like pycodestyle, or you'll end up with quite a mess.

Next, you should add a configuration section to your pyproject.toml to tell basedpyright where to look for your virtual environment.

[tool.pyright]
venv=".venv"
venvPath="."

You can also do this in pyrightconfig.json file if, unlike me, you do not already feel completely overrun with config files for different Python development tools.

Installing basedpyright as a language server

One very nice thing about basedpyright over pyright is that it builds the nodejs dependency as a wheel, so you can be assured that basedpyright should work on your machine regardless of whether you have nodejs installed.

For isolation, it is usually a good idea to install executable Python packages using pipx instead of pip. Let's go ahead and do that .

pipx install basedpyright

For a sanity check, consider running

basedpyright --version

Installing basedpyright also gives you access to thebasedpyright-langserver command, but that's not really written for users to interact with, so if you runbasedpyright-langserver orbasedpyright-langserver --version or something, you'll get a nodejs stack trace.

Configuring emacs to use basedpyright-langserver

I'll assume you as the reader know how to install packages from MELPA and have a preferred way to do it. Here are all the packages you need:

• company
• lsp-mode
• lsp-pyright
• lsp-ui
• python-mode

Get those installed and then open your ~/.emacs or your ~/.emacs.d/init.el and add the following:

;; lsp global settings
(add-hook 'after-init-hook 'global-company-mode)
(setq lsp-auto-guess-root t)

;; python
(require 'lsp-mode)
(setq lsp-pyright-langserver-command "basedpyright")
(add-hook 'python-mode-hook (lambda () (require 'lsp-pyright) (lsp)))

That should be all you need.

A general tip for debugging lsp-mode

If you feel like you've set everything up correctly and you're still having trouble getting lsp-mode to find packages that should be available in Poetry, one thing you might try is to go in and delete your ~/.emacs.d/.lsp-session-v1. This will have the effect of causing lsp-mode to forget about the project root and force it to look for it again.

Happy coding!

I hope this has given you a good head start on your Python development environment. If you have any questions, well, I'm a beginner with all this, and I probably can't help you, but I will consider merge requests if you have any extra tips or tricks for using basedpyright with emacs.

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