Eglot based Emacs Python IDE

2018-12-05

This post is now a bit outdated an updated post is here.

In my Emacs rabbit hole I mentioned in my previous post, I decided to work on improving my Python development workflow. I recently found the Eglot package for running a LSP in Emacs.

The most vanilla setup for Eglot is just M-x eglot in a buffer editing a python file. This works wonderfully if the executable for the Python Language Server (pyls) is found. This works because Eglot defines a list of server programs by default. See this list with M-: eglot-server-programs

Project Editing

I have a few python virtual/Anaconda environments I like to work with. This is what .dir-locals.el is for:

((python-mode . ((eglot-server-programs    . ((python-mode "/path/to/env/bin/pyls")))
                 (python-shell-interpreter . "/path/to/env/bin/python")
                 (company-backends         . (company-capf)))))

where /path/to/env is the path to a virtual environment or Anaconda environment (that of course has python-language-server installed). I also define the path to my Python executable for Emacs' builtin python.el. By default, company-backends includes company-capf for completion-at-point, but I want to make sure that's what is used because Eglot provides completion-at-point. Eglot also has pyls as a python-mode entry by default, but not to the virtual environment I want to use; this is why I manually define the list of server programs.

When I open a buffer in the project I want to work in, I just call M-x eglot and I'm up and running.

Non-project Editing

If I'm not editing in a project that has an associated virtual environment, I rely on some "sensible defaults" in my Emacs init file:

(defvar ddavis-default-pyls "~/software/Python/anaconda3/bin/pyls"
  "define a default pyls to be used")

This way I have a default pyls executable from my base Anaconda environment (which is potentially different on different machines). I then have a couple of functions to handle default Eglot python environments, where I:

Make use-package install Eglot if necessary.
Make sure company-capf is at the front of company-backends.
Make sure I add an Eglot server program entry pointing to my base Anaconda pyls to the front of the eglot-server-programs list.
Add the desired hook.

(use-package eglot
  :ensure t)

(defun dd/python-eglot-enable ()
  "set variables and hook for eglot python IDE"
  (interactive)
  (setq company-backends
        (cons 'company-capf
              (remove 'company-capf company-backends)))
  (add-to-list 'eglot-server-programs
               `(python-mode ,ddavis-default-pyls))
  (add-hook 'python-mode-hook 'eglot-ensure))

(defun dd/python-eglot-disable ()
  "remove hook for eglot python"
  (interactive)
  (remove-hook 'python-mode-hook 'eglot-ensure))

I just bring company-capf to the front of the company-backends list, and add my desired Anaconda based pyls to front of the eglot-server-programs list.