lonesnake

lonesnake is a zero-config Bash tool that generates self-contained Python environments with a single command. Each environment fits in a single directory, including a CPython interpreter built from source and a venv. When a capricious environment breaks, you can just delete the directory and generate a new one easily.

It enables you to generate isolated environments not only for projects, but also for global environments or Docker images. It integrates seamlessly with IDEs (VS Code, PyCharm) and dependency management tools (Poetry, pip-tools). It does not impose shell init scripts, so you can activate environments with the method of your choice.

What are the limitations of lonesnake?

• accepts only a single interpreter version per project and per global environment
• supports CPython 3.7+ but not older CPython versions nor alternative interpreters like Pypy
• runs on macOS and Linux, but not Windows
• consumes more disk space than tools that store interpreters in a centralized location

I designed lonesnake to be much easier to understand for the average developer than the centralized tools out there. I deliberately renounced many features to keep the code structure simple. But if lonesnake is too basic for you, feel free to adopt the well-established pyenv or asdf.

installation

macOS installation with Brew

• Step 1: brew tap pwalch/lonesnake
• Step 2: brew install lonesnake

Linux installation with package manager and curl

Step 1: install the CPython build dependencies and curl, depending on your OS

# The instructions below are taken from the pyenv Wiki and the python.org dev guide.
# Please check them out if you need more details or if you are using a different OS.
# https://github.com/pyenv/pyenv/wiki#suggested-build-environment
# https://devguide.python.org/setup/#install-dependencies

# Ubuntu/Debian/Mint
sudo apt-get update && sudo apt-get install -y \
  make build-essential libssl-dev zlib1g-dev libbz2-dev libreadline-dev \
  libsqlite3-dev wget curl llvm libncursesw5-dev xz-utils tk-dev \
  libxml2-dev libxmlsec1-dev libffi-dev liblzma-dev

# Fedora
sudo dnf install \
  curl make gcc zlib-devel bzip2 bzip2-devel readline-devel \
  sqlite sqlite-devel openssl-devel tk-devel libffi-devel xz-devel

# Arch Linux
sudo pacman -S --needed curl base-devel openssl zlib xz

Step 2: download lonesnake to ~/.local/bin

mkdir -p ~/.local/bin && \
  curl -sL -o ~/.local/bin/lonesnake https://github.com/pwalch/lonesnake/releases/download/0.31.0/lonesnake && \
  chmod u+x ~/.local/bin/lonesnake

• make sure you have export PATH="$HOME/.local/bin:$PATH" in your .bashrc (Bash) or .zshrc (ZSH), and open a new shell
• check that the script is accessible with lonesnake --help

usage

example commands

• lonesnake
  • generates an environment with the latest CPython version, in the .lonesnake directory at the root of the current working directory
• lonesnake --py 3.11
  • same, but with the latest patch of CPython 3.11
• lonesnake --py 3.11.0
  • same, but with exactly CPython 3.11.0

If the .lonesnake directory already exists, lonesnake asks for confirmation before deleting it.

automated activation

project activation with direnv

To activate a lonesnake environment when entering a project directory, you can bring your own shell auto-load tool. If you are undecided, I recommend direnv.

install direnv and register its hook

# macOS
brew install direnv

# Ubuntu/Debian/Mint
sudo apt-get install direnv

# Fedora
sudo dnf install direnv

# Archlinux
sudo pacman -S direnv

• Bash: in your ~/.bashrc, append eval "$(direnv hook bash)"
• ZSH: in your ~/.zshrc, append eval "$(direnv hook zsh)"

generate the project lonesnake environment and enable auto-activation

• start a new shell then cd YOUR_PROJECT
• lonesnake
• touch .envrc then fill it with this code

# lonesnake auto-activation for the project directory
lonesnake_dir="${PWD}/.lonesnake"
PATH_add "${lonesnake_dir}/venv/bin"
export VIRTUAL_ENV="${lonesnake_dir}/venv"

# Solve errors involving "Python.h not found" when building
# Python extensions with a lonesnake environment.
parent_include_dir="${lonesnake_dir}/interpreter/usr/local/include"
if [[ -d "$parent_include_dir" ]]; then
  include_dir_name=$(find "$parent_include_dir" \
    -mindepth 1 -maxdepth 1 -type d -name "python3.*" \
    -exec basename {} \;)
  path_add CPATH "${parent_include_dir}/${include_dir_name}"
fi

• direnv allow
• check that which python prints your project's .lonesnake/venv directory

ℹ️ In case of trouble, you can get rid of the lonesnake environment by running rm -rf .lonesnake .envrc at the root of your project. Make sure to open a new shell for the change to take effect.

Tips

If you have lonesnake-kit, you can use lonesnake-kit project --direnv to automatically populate .envrc.

If you find yourself pasting into .envrc files often, automate it with this function for your ~/.bashrc or ~/.zshrc.

# Print direnv activation instructions for lonesnake
# Usage: lonesnake-print-activation >> .envrc
function lonesnake-print-activation() {
cat << EOM
# lonesnake auto-activation for the project directory
lonesnake_dir="\${PWD}/.lonesnake"
PATH_add "\${lonesnake_dir}/venv/bin"
export VIRTUAL_ENV="\${lonesnake_dir}/venv"

# Solve errors involving "Python.h not found" when building
# Python extensions with a lonesnake environment.
parent_include_dir="\${lonesnake_dir}/interpreter/usr/local/include"
if [[ -d "\$parent_include_dir" ]]; then
  include_dir_name=\$(find "\$parent_include_dir" \
    -mindepth 1 -maxdepth 1 -type d -name "python3.*" \
    -exec basename {} \;)
  path_add CPATH "\${parent_include_dir}/\${include_dir_name}"
fi
EOM
}

To show a prefix in your shell prompt indicating an active lonesnake venv (e.g. 🐍venv-3.11.0), take inspiration from this example code for your ~/.bashrc or ~/.zshrc.

show_lonesnake_venv_prefix () {
  local cpython_path="$PWD/.lonesnake/venv/bin/python"
  # If the venv is activated, print the prompt prefix
  if [[ -x "$cpython_path" ]] && \
      [[ "$(which python)" == "$cpython_path" ]]; then
    local cpython_version="$(python --version | grep -Eo '[0-9]+\.[0-9]+\.[0-9]+')"
    echo "🐍venv-${cpython_version} "
  fi
}
PS1='$(show_lonesnake_venv_prefix)'"$PS1"

project dependency management

Provided you have configured direnv as in the previous section, dependency management tools integrate seamlessly into lonesnake venvs.

pip-tools

pip-tools' sync command installs packages in the current venv. Therefore, all packages are installed in the .lonesnake venv directory by default:

• cd YOUR_PROJECT
• pip install pip-tools
• pip-sync PINNED_COMPILED_REQUIREMENTS

Poetry

You can integrate Poetry into the .lonesnake directory by specifying the POETRY_VIRTUALENVS_PATH environment variable:

• cd YOUR_PROJECT (where your pyproject.toml is)
• append the following to your .envrc:

export POETRY_VIRTUALENVS_PATH="${PWD}/.lonesnake/poetry_virtualenvs"

• direnv allow
• pip install poetry
• poetry install
• check with poetry debug that the "Virtualenv Path" is in a child directory of .lonesnake/poetry_virtualenvs

Tips

If you have lonesnake-kit, note that lonesnake-kit project --direnv populates the Poetry environment variables in .envrc.

ℹ️ In case of trouble, you can get rid of the Poetry virtualenvs using rm -rf .lonesnake/poetry_virtualenvs. Make sure to open a new shell for the change to take effect.

project IDE support

Visual Studio Code (VS Code)

Auto-Activation:

• open a project directory that contains a lonesnake environment at its root
• click File > Preferences > Settings and then go to Workspace and search for python.defaultInterpreterPath
• set this path to ${workspaceFolder}/.lonesnake/venv/bin/python
• press CMD/CTRL + SHIFT + P or click View > Command Palette, then choose Python: Select Interpreter
• choose Use Python from `python.defaultInterpreterPath` setting
  • note that after the word setting, you should see ./.lonesnake/venv/bin/python
• when you open the integrated terminal, VS Code should now be sourcing .lonesnake/venv/bin/activate

File Exclusion:

• click File > Preferences > Settings and then go to User and search for files.exclude
• click Add Pattern and register **/.lonesnake

If you have lonesnake-kit, note that lonesnake-kit project --vscode populates the settings.json of the workspace in the working directory.

PyCharm

• open a project directory that contains a lonesnake environment at its root
• click File > Settings > Project: YOUR_PROJECT > Python Interpreter
• click Add Interpreter > Add Local Interpreter...
• in Virtualenv Environment
  • set Environment to Existing
  • as Interpreter, pick .lonesnake/venv/bin/python from your project
  • click OK
• click OK, then wait for the environment to be indexed
• when you create a new Run/Debug configuration, the Python interpreter field should point to the lonesnake environment

user-wide global auto-activation

To activate a lonesnake environment user-wide when opening a new shell, you can generate one at the root of your HOME and register it in your .bashrc or .zshrc.

• cd ~
• lonesnake
• in your .bashrc (Bash) or .zshrc (ZSH), append the following:

# global lonesnake auto-activation
export PATH="${HOME}/.lonesnake/venv/bin:${PATH}"

• exit your shell and start a new one
• check that which python points to your lonesnake environment

Tips

ℹ️ In case of trouble, you can get rid of the lonesnake environment by removing the export statements from your .bashrc or .zshrc and running rm -rf ~/.lonesnake. Make sure to open a new shell for the change to take effect.

Pip safeguard shim against accidental pollution of global environment

Sometimes, you will forget to create a project-specific lonesnake environment or to configure its auto-activation. In this case, all pip install commands you want to run will be forwarded to the global environment and pollute its package list.

To safeguard against this pollution, you can intercept pip commands by adding the following shim to your ~/.bashrc or ~/.zshrc:

# Safeguard shim against accidental 'pip install' to
# the global lonesnake environment.
# Call '~/.lonesnake/venv/bin/pip' to bypass.
function pip () {
  if [[ -z "$VIRTUAL_ENV" ]]; then
    echo "[ERROR] Cannot run 'pip' command outside" \
      "of a VIRTUAL_ENV."
    return 1
  fi

  local active_pip=""
  if ! active_pip="$(whence -p pip)"; then
    echo "[ERROR] There is no 'pip' command in PATH:" \
      "${PATH}"
    return 1
  fi

  local global_pip=""
  global_pip="${HOME}/.lonesnake/venv/bin/pip"
  if [[ -f "$global_pip" ]] && \
      [[ "$active_pip" == "$global_pip" ]]; then
    echo "[ERROR] Cannot run 'pip' command with global" \
        "environment: ${global_pip}"
    return 1
  fi

  command pip "$@"
}

pipx support

After setting up a global lonesnake environment, you should install pipx to manage Python command-line tools. In the same spirit as lonesnake, pipx installs all tools in isolated venvs so they don't break each other or interfere with the global one. To integrate pipx:

• append these lines to your .bashrc or .zshrc:

# By default, pipx stores its files in "~/.local/pipx" and "~/.local/bin", but we
# configure it to use sub-directories of the lonesnake global environment:
# "~/.lonesnake/pipx_bin" and "~/.lonesnake/pipx_home". Thanks to this,
# we keep everything related to the global environment in the same place.
export PIPX_HOME="${HOME}/.lonesnake/pipx_home"
export PIPX_BIN_DIR="${HOME}/.lonesnake/pipx_bin"
export PATH="${PIPX_BIN_DIR}:${PATH}"

• exit your shell and start a new one
• ~/.lonesnake/venv/bin/pip install pipx
• from now on, use pipx install to install Python CLI tools such as httpie

Tips

ℹ️ In case of trouble, you can get rid of your pipx installation by running rm -rf ~/.lonesnake/pipx_* and ~/.lonesnake/venv/bin/pip uninstall pipx. Make sure to open a new shell for the change to take effect.

optional kit

If you use direnv, Poetry, VS Code or some other popular tools, you might find lonesnake-kit useful. This program creates a new lonesnake environment and then automatically populates .envrc, .vscode/settings.json, etc... to configure your projects faster.

Before using lonesnake-kit, make sure to read the instructions for vanilla lonesnake. Once you are familiar with it, check out available integrations with lonesnake-kit --help.

kit macOS installation with Brew

brew install lonesnake-kit

kit Linux installation with curl

mkdir -p ~/.local/bin && \
  curl -sL -o ~/.local/bin/lonesnake-kit https://github.com/pwalch/lonesnake/releases/download/0.31.0/lonesnake-kit && \
  chmod u+x ~/.local/bin/lonesnake-kit

lonesnake environment structure

This .lonesnake directory includes a Python interpreter built from source, as well as a venv:

• interpreter directory includes usr/local/bin, usr/local/include, etc...
• venv directory includes bin, include, pyvenv.cfg etc... It is created by the interpreter above.

Behind the scenes, lonesnake takes advantage of cache directories for the CPython source code and build files, located at ~/.cache/lonesnake/X.Y.Z/ where X.Y.Z is the Python version (e.g. 3.11.0). Cache directories enable us to skip the compilation step when CPython was already compiled for the requested version.

lonesnake environment construction

To construct the .lonesnake directory, lonesnake follows the standard CPython build process, but with extra sanity checks:

• before CPython build
  • check if there is Internet access to python.org, otherwise you cannot download anything
• during CPython build
  • error out if Python could not be compiled with OpenSSL, as it would make Pip unusable
  • on macOS, use Brew's OpenSSL and LZMA libraries instead of system ones for consistency
• after generating venv
  • upgrade Pip to latest version
  • install setuptools + wheel as they are pre-requisites for many other packages