Virtual-Environments.md

Virtual Environments

Installing python packages globally isn't recommended. Instead, you should install Molten python dependencies in a virtual environment using venv.

The main reason is that working without a virtual environment gets really messy really quickly, and can just be impossible if you work on multiple python projects that have different dependency version requirements. If you want to use this plugin with venv, you shouldn't have to add all of Molten's dependencies to your project's virtual environment, that's what this guide is for.

To facilitate the creation and activation of 'global' virtual environments, I use a venv wrapper. I would definitely recommend a wrapper script of some kind if you are a python dev. If you're just installing these deps to use Molten with a non-python kernel, you can skip the wrapper without much worry.

Create a Virtual Environment

We'll create a virtual environment called neovim that will contain all of our Molten (and other remote plugin dependencies).

Using the wrapper:

mkvenv neovim # create a new venv called neovim
venv neovim # activate the virtual environment

Not using the wrapper

mkdir ~/.virtualenvs
python -m venv ~/.virtualenvs/neovim # create a new venv
# note, activate is a bash/zsh script, use activate.fish for fish shell
source ~/.virtualenvs/neovim/bin/activate # activate the venv

Install Dependencies

Make sure your venv is active (you can test with echo $VIRTUAL_ENV) then you can install the python packages that relate to the types of output you want to render. Remember, pynvim and jupyter_client are 100% necessary, everything else is optional. You can see what each package does in the readme.

pip install pynvim jupyter_client cairosvg plotly kaleido pnglatex pyperclip

Point Neovim at this Virtual Environment

add this to your neovim configuration

vim.g.python3_host_prog=vim.fn.expand("~/.virtualenvs/neovim/bin/python3")

Install The Kernel In a Project Virtual Environment

In your project virtual environment (here named "project_name"), we need to run:

venv project_name # activate the project venv
pip install ipykernel
python -m ipykernel install --user --name project_name

Now, launch Neovim with the project venv active. You should be able to run :MoltenInit project_name to start a Kernel for your project virtual environment.

Automatically launch the correct Kernel

Assuming you followed the steps above, you may now have multiple python kernels all with names that match their corresponding virtual environment. Calling :MoltenInit and selecting an option all the time is kinda annoying, instead, we can add this mapping, which allows you to automatically initialize the correct kernel.

vim.keymap.set("n", "<localleader>ip", function()
  local venv = os.getenv("VIRTUAL_ENV")
  if venv ~= nil then
    -- in the form of /home/benlubas/.virtualenvs/VENV_NAME
    venv = string.match(venv, "/.+/(.+)")
    vim.cmd(("MoltenInit %s"):format(venv))
  else
    vim.cmd("MoltenInit python3")
  end
end, { desc = "Initialize Molten for python3", silent = true })