Start and attach to neovim in same python file

Question

I have a working prototype for some kind of linux-based neovim-app. Sole functionality is "vsplit if 'k' is pressed". It is based on tarruda's nvim-terminal-edit-py.

It is started through start_nvim.sh:

#!/bin/bash
NVIM_LISTEN_ADDRESS='/tmp/nvim' /usr/bin/nvim &
./myapp.py

myapp.py is

#!/usr/bin/env python
import os, sys, time, subprocess
from neovim import attach

tf = '/tmp/nvim'

env = dict(os.environ)
env['NVIM_LISTEN_ADDRESS'] = tf

#os.execvpe("nvim", ["nvim"], env)
#subprocess.Popen(["/usr/bin/nvim"], env=env)
#subprocess.call(['/usr/bin/nvim', '&'], env=env)

nvim = attach("socket", path=tf)

def key_subscribe(key, to):
    cid = nvim.channel_id                                                                                                               
    nvim.command( ('nnoremap <silent> <buffer> %s ' + ':call rpcnotify(%d, "keypress", "%s")<cr>') % (key, cid, to))


def _request_cb(*args):
    pass


def _notification_cb(*args):
    nvim.command('vsplit')


def _setup_cb():
    key_subscribe('k', 'up')


nvim.run_loop(_request_cb, _notification_cb, _setup_cb)

How to start /usr/bin/nvim from within myapp.py, so that start_nvim.sh is not necessary?

I did try various things.

Uncommenting the respective line in myapp.py and directly executing ./myapp.py:

execvpe does start nvim, but if I press k no vsplit is triggered.

Popen and call yield

Traceback (most recent call last):
  File "./myapp.py", line 18, in <module>
    nvim = attach("socket", path=tf)
...
FileNotFoundError: [Errno 2] No such file or directory

Obviously, Popen/call didn't pass /tmp/nvim to nvim.

Answer 1

Your problem is that you're starting a Neovim subprocess and it's blocking before processing the rest of your script. When you quit Neovim, the rest of the script executes well after the file socket has outlived its use to Neovim.

You will need to start it from a thread so that the rest of the script can execute.

#!/usr/bin/env python
import os
import time
import threading
import subprocess

from neovim import attach

tf = '/tmp/nvim'


def start_neovim():
    env = dict(os.environ)
    env['NVIM_LISTEN_ADDRESS'] = tf
    subprocess.call(['/usr/bin/nvim'], env=env)


t = threading.Thread(target=start_neovim)
t.daemon = True
t.start()

# Give Neovim time to start
time.sleep(1)

nvim = attach("socket", path=tf)


def key_subscribe(key, to):
    cid = nvim.channel_id
    nvim.command(('nnoremap <silent> <buffer> %s ' + ':call rpcnotify(%d, "keypress", "%s")<cr>') % (key, cid, to))


def _request_cb(*args):
    pass


def _notification_cb(*args):
    nvim.command('vsplit')


def _setup_cb():
    key_subscribe('k', 'up')


nvim.run_loop(_request_cb, _notification_cb, _setup_cb)

I hope you're just doing this as an exercise. Configuring key bindings using the RPC interface is a little silly considering you still have to use Vim's language to do it.

The more common approach is to use .vim scripts to setup the keybindings and API, then use Python for things that aren't practical to do in Vim such as networking or long running asynchronous work.