Setting up Python for Neovim

Tommy Allen edited this page Apr 16, 2016 · 3 revisions
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Setting up Python for Neovim

Neovim requires a package to be installed for Python plugins to work. You really should read :h nvim-python to supplement the info on this page.

Table of Contents

A brief overview of Neovim + Python

The main advantages of using Python in plugins is that it enables plugins to have access to network sockets, and perform long-running or expensive operations in the background without freezing the Vim UI. This is the reason it is commonly used with completion plugins.

Vim plugins are able to execute Python code when Vim is compiled with Python support. However, default system installations of Vim that are compiled with Python versions that are considered to be the stable default for the OS, which usually meant Python 2.6 or 2.7 until recently. Additionally, Vim could only be compiled with Python 2 or Python 3, not both. Re-compiling Vim to include newer versions is a non-trivial task and it would put an undue burden on users if plugins required Python 3.

Neovim resolves these limitations by providing a bridge to your system's Python installations. It requires a Python package to be installed, which still puts a burdern on the user, but it is arguably easier than re-compiling Vim.

Requirements

Each Python interpreter that is used with Neovim will require the neovim package.

deoplete.nvim requires Python 3 to be installed. By extension, deoplete-jedi does, too. It is recommended that Python 3.3+ is used, but any Python version greater than 3.1 should work.

Simple Setup

If you do light Python development, or the extent of your Python use is limited to Neovim, the basic installation instructions will be sufficient.

:h nvim-python suggests the use of sudo pip install neovim for system-wide availability. It's an acceptable solution if you are certain that your Python environment will be unaffected. Read the following section before you consider using sudo: Why you shouldn't use sudo

It is recommended to use the --user flag when installing the neovim package:

pip2 install --user neovim
pip3 install --user neovim

The --user flag installs neovim in a directory within your home directory. The limitation with this is that every user account on the system will need to perform this step. You can confirm the location and that your environment permits user packages by running: python -m site

Using Virtual Environments

If you do heavy Python development, you will most likely prefer using a virtual environment. deoplete-jedi will display completions for your current shell's Python interpreter (run: which python to determine this). This includes the Python interpreter that are made active using a virtualenv.

If you are already using virtualenv for all of your work, it is recommended that you use separate virtual environments for Neovim, and only Neovim. This will remove the need to install the neovim package in each virtual environment. The following examples uses pyenv. There are tips below for installing and using pyenv without much effort. TODO: add instructions for pyvenv and virtualenv

pyenv install 2.7.11
pyenv install 3.4.4

pyenv virtualenv 2.7.11 neovim2
pyenv virtualenv 3.4.4 neovim3

pyenv activate neovim2
pip install neovim
pyenv which python  # Note the path

pyenv activate neovim3
pip install neovim
pyenv which python  # Note the path

# The following is optional, and the neovim3 env is still active
# This allows flake8 to be available to linter plugins regardless
# of what env is currently active.  Repeat this pattern for other
# packages that provide cli programs that are used in Neovim.
pip install flake8
ln -s `pyenv which flake8` ~/bin/flake8  # Assumes that $HOME/bin is in $PATH

Now that you've noted the interpreter paths, add the following to your init.vim file:

let g:python_host_prog = '/full/path/to/neovim2/bin/python'
let g:python3_host_prog = '/full/path/to/neovim3/bin/python'

Tips for using pyenv

  • Ensure you have the prerequisites installed.
  • Installing pyenv with homebrew is unreliable. Use pyenv-installer instead.
  • There is a final step that's printed to the terminal after installing pyenv and it's important!
  • To confirm you have pyenv correctly installed, run which pyenv. It should print a shell function, not a file path.
  • Run pyenv doctor to avoid surprises.
  • pyenv global can be thought of as altering the $PATH to include the specified versions' bin directory. This only works while pyenv is active.
  • pyenv shell is the same as above, but for the current session.
  • pyenv local is the same as above, but it writes a .python-version file in the current directory. It allows the specified versions to be automatically set when you enter the directory, and unset when you leave it. Very convenient for projects.
  • You will want to add .python-version to your global .gitignore file.
  • pyenv shell --unset will reset the session's Python versions.
  • pyenv activate venvname differs from pyenv shell venvname in that only one $VIRTUAL_ENV can be active at a time.
  • pyenv deactivate deactivates the virtual environment.
  • pyenv versions lists the versions you have installed. system is a special case pointing to Python versions that were originally found in $PATH. Virtual environment names are listed as versions.

Why you shouldn't use sudo

Unless you know what you're doing, the system installed Python interpreters should remain pristine and only contain packages that were installed via the OS's package manager (read: not pip). sudo in front of pip install should make you cringe any time it's recommended.

Some distros use separate locations for system packages and user packages, but the potential to mess things up is increased when you use sudo. On distros that don't make a distinction between system and user packages, it's possible to upgrade system packages with sudo pip install -U. Or the reverse could happen and you'll downgrade packages installed with pip. There is also the issue of non-Python system packages that may require the specific versions of Python packages that were built for the distro. The point is, you will have two package managers competing to decide what's new or old.

A very common example of what can go wrong: sudo pip install --upgrade pip. It is a problem many Python developers encounter. This problem occurs more than it should and renders all Python programs installed in the system bin directories to be broken.

If you can't honestly say that you know how Python packages are laid out or what your system's Python dependencies are, and enjoy having a stable, error-free Python installation, leave the system Python installations alone.