venv.fish - Automatically activate/deactivate virtualenv in fish shell

venv.fish

# Based on https://gist.github.com/bastibe/c0950e463ffdfdfada7adf149ae77c6f
# Changes:
# * Instead of overriding cd, we detect directory change. This allows the script to work
#   for other means of cd, such as z.
# * Update syntax to work with new versions of fish.
# * Handle virtualenvs that are not located in the root of a git directory.

function __auto_source_venv --on-variable PWD --description "Activate/Deactivate virtualenv on directory change"
  status --is-command-substitution; and return

  # Check if we are inside a git directory
  if git rev-parse --show-toplevel &>/dev/null
    set gitdir (realpath (git rev-parse --show-toplevel))
    set cwd (pwd -P)
    # While we are still inside the git directory, find the closest
    # virtualenv starting from the current directory.
    while string match "$gitdir*" "$cwd" &>/dev/null
      if test -e "$cwd/.venv/bin/activate.fish"
        source "$cwd/.venv/bin/activate.fish" &>/dev/null 
        return
      else
        set cwd (path dirname "$cwd")
      end
    end
  end
  # If virtualenv activated but we are not in a git directory, deactivate.
  if test -n "$VIRTUAL_ENV"
    deactivate
  end
end

I made a plugin called autopy.fish for the Fish Shell that automatically activates your Python virtual environment (venv or Poetry) when you cd into a project directory—and deactivates any previously active environment. It detects .venv or pyproject.toml, works with Git repos (uses the repo root as the project dir), and is designed to be fast and lightweight, running on every directory change. Install with Fisher or manually.
Check it out here: https://github.com/SpaceShaman/autopy.fish