pyls is a language server for Python. lsp-mode is an implementation of the LSP protocoll for emacs. It has the advantage that it offers the same functionality (as far as it's implemented in the LSP server) for all programming languages.

pyls is aware of Python virtual environments. The plugins used by pyls are either independent of the environment or are also virtual environment aware. Thje exception to this is pylint, whic performs a variaty of checks and needs to be aware of virtual environment so that it can resolve imported modules.

You can of course intall pylint in every virtual environment you are using, but when you work on more then one or two projects this can cause some maintainance load.

So i was looking how to configure emacs, virtial environments, and pylint in such a way that you can use a globally install pylint ion different virtual environments, without re-installing and without the need to upgrade all installations in all the virtual environments instead of just the system wide installation.

called pylint`_calls `pylint exec witht he help of elpylint module. This starts the pylint executable, but witout setting it up correctly. Using the pyvenv package of emacs to manage yourt virtualenvironments and the init_hook in pylintrc this can be corrected.

1. make sure there is an activate_this.py file in the virtualenv. It's missing if the virtualenv was created using pyhton -m venv <name> instead of virtualenv If not a copy is in this directory. Copy it in the bin directory of the virtual environment

2. Create a pylinrc.py file somewhere. I put it in my ~/bin folder. The file is a simple wrapper to execute the activate_this.py file. This is only necessary, because the .pylintrc file does not allow multiline content. And I have not found an easy way to implement this in one line (no '\' allowed) Here's the content of the file:

   import sys, os
   
   if 'VIRTUAL_ENV' not in os.environ:
       sys.exit(0)
   
   ve = os.environ['VIRTUAL_ENV']
   ve in sys.path or sys.path.insert(0, ve)
   activate_this = os.path.join(os.path.join(ve, 'bin'), 'activate_this.py')
   exec(open(activate_this).read(), dict(__file__=activate_this))
   

4. Create .pylintrc file

   pylint --generate-rcfile > ~/.pylintrc
   

   should do the trick. Change the init-hook in this file to

   init-hook="import imp, os; imp.load_source('import_hook',os.path.join(os.env.get('HOME'), 'bin', 'pylintrc.py'))``
   

To automatically switch to the correct virtual environment when working on a python project I put the following into the .dir-locals.el file in the root dir of the project.

;;; Directory Local Variables
;;; For more information see (info "(emacs) Directory Variables")

((python-mode
  (eval . (pyvenv-mode t))
  (pyvenv-activate . "path to the virtual environment")))