The Python Launcher for Unix

Launch your Python interpreter the lazy/smart way!

This project is an implementation of the py command for Unix-based platforms (with some potential experimentation for good measure 😉).

The goal is to have py become the cross-platform command that Python users typically use to launch an interpreter while doing development. By having a command that is version-agnostic when it comes to Python, it side-steps the "what should the python command point to?" debate by clearly specifying that upfront (i.e. the newest version of Python that can be found). This also unifies the suggested command to document for launching Python on both Windows as Unix as py has existed as the preferred command on Windows since 2012 with the release of Python 3.3.

Typical usage would be:

py -m venv .venv
py ...  # Normal `python` usage.

This creates a virtual environment in a .venv directory using the latest version of Python installed. Subsequent uses of py will then use that virtual environment as long as it is in the current (or higher) directory; no environment activation required (although the Python Launcher supports activated environments as well)!

A non-goal of this project is to become the way to launch the Python interpreter all the time. If you know the exact interpreter you want to launch then you should launch it directly; same goes for when you have requirements on the type of interpreter you want (e.g. 32-bit, framework build on macOS, etc.). The Python Launcher should be viewed as a tool of convenience, not necessity.

Installation

Linux

Linuxbrew

brew install python-launcher

https://formulae.brew.sh/formula/python-launcher

Arch

yay -S python-launcher

https://aur.archlinux.org/packages/python-launcher

Fedora

sudo dnf install python-launcher

Requires Fedora 34 or higher.

https://src.fedoraproject.org/rpms/rust-python-launcher/

RISC-V

1. Download python_launcher-1.0.0-riscv64gc-unknown-linux-gnu.tar.xz:

curl --location --remote-name https://github.com/brettcannon/python-launcher/releases/download/v1.0.0/python_launcher-1.0.0-riscv64gc-unknown-linux-gnu.tar.xz

2. Install into, e.g. /usr/local:

tar --extract --strip-components 1 --directory /usr/local --file python_launcher-1.0.0-riscv64gc-unknown-linux-gnu.tar.xz

AArch64

1. Download python_launcher-1.0.0-aarch64-unknown-linux-gnu.tar.xz:

curl --location --remote-name https://github.com/brettcannon/python-launcher/releases/download/v1.0.0/python_launcher-1.0.0-aarch64-unknown-linux-gnu.tar.xz

2. Install into, e.g. /usr/local:

tar --extract --strip-components 1 --directory /usr/local --file python_launcher-1.0.0-aarch64-unknown-linux-gnu.tar.xz

x86-64

1. Download python_launcher-1.0.0-x86_64-unknown-linux-gnu.tar.xz:

curl --location --remote-name https://github.com/brettcannon/python-launcher/releases/download/v1.0.0/python_launcher-1.0.0-x86_64-unknown-linux-gnu.tar.xz

2. Install into, e.g. /usr/local:

tar --extract --strip-components 1 --directory /usr/local --file python_launcher-1.0.0-x86_64-unknown-linux-gnu.tar.xz

macOS

Homebrew

brew install python-launcher

https://formulae.brew.sh/formula/python-launcher

Apple Silicon

1. Download python_launcher-1.0.0-aarch64-apple-darwin.tar.xz:

curl --location --remote-name https://github.com/brettcannon/python-launcher/releases/download/v1.0.0/python_launcher-1.0.0-aarch64-apple-darwin.tar.xz

2. Install into, e.g. /usr/local:

tar --extract --strip-components 1 --directory /usr/local --file python_launcher-1.0.0-aarch64-apple-darwin.tar.xz

x86-64

1. Download python_launcher-1.0.0-x86_64-apple-darwin.tar.xz:

curl --location --remote-name https://github.com/brettcannon/python-launcher/releases/download/v1.0.0/python_launcher-1.0.0-x86_64-apple-darwin.tar.xz

2. Install into, e.g. /usr/local:

tar --extract --strip-components 1 --directory /usr/local --file python_launcher-1.0.0-x86_64-apple-darwin.tar.xz

NetBSD

x86-64

1. Download python_launcher-1.0.0-x86_64-unknown-netbsd.tar.xz:

curl --location --remote-name https://github.com/brettcannon/python-launcher/releases/download/v1.0.0/python_launcher-1.0.0-x86_64-unknown-netbsd.tar.xz

2. Install into, e.g. /usr/local:

tar --extract --strip-components 1 --directory /usr/local --file python_launcher-1.0.0-x86_64-unknown-netbsd.tar.xz

Any OS supporting Rust

Crates.io

cargo install python-launcher

https://crates.io/crates/python-launcher

Source

cargo install --path .

https://github.com/brettcannon/python-launcher

Documentation

The general control flow for finding the appropriate Python executable is the following (with Python 3.6, Python 3, and the newest version of Python installed as examples):

graph TD
    start[py ...] --> major_minor[-3.6]
    start --> major_only[-3]
    start --> best[No option specified]

    major_minor --> $PATH

    major_only --> PY_PYTHON3

    $PATH --> exec

    best --> env_var{$VIRTUAL_ENV}

    env_var --> venv_dir{.venv}

    venv_dir --> shebang{#! ...}
    venv_dir --> exec

    shebang --> PY_PYTHON([$PY_PYTHON])
    shebang --> PY_PYTHON3([$PY_PYTHON3])

    PY_PYTHON3 --> $PATH
    PY_PYTHON --> $PATH
    shebang --> $PATH

    env_var --> exec[Execute Python]

See the man page or the top section of py --help for more details.

See the API docs for using this project to build your own custom Launcher.

FAQ

Why isn't the Python Launcher finding all of my Python versions installed via Homebrew?

If you have multiple installs of Python via Homebrew but they are not all being found (as verified via py --list), chances are Homebrew didn't symlink an installation due to the python symlink already being defined. For each installation you are missing you will need to tell Homebrew to ignore the conflict so that the version-specific python symlink gets created.

For instance, if your Python 3.10 installation isn't being found (due to python3.10 not existing), try running:

brew link --overwrite python@3.10

That will critically symlink the python3.10 command. It will also overwrite what python3 points at, so you may want to run the brew link command for the newest version of Python you have installed last.

How do I have Starship use the Python Launcher to display the Python version?

Add the following to your Starship configuration file:

[python]
python_binary = ["py"]
# The following isn't necessary, but convenient.
detect_folders = [".venv"]

By using the Launcher with Starship, your prompt will tell you which Python version will be used if you run py. Since the Launcher supports virtual environments, the prompt will properly reflect both what global install of Python will be used, but also the local virtual environment.

How do I get a table of Python executables in Nushell?

py --list | lines | split column "│" version path | str trim

Do note that the character that is being split on is not the traditional U+007C/"Vertical Line"/pipe character (|), but U+2502/"Box Drawings Light Vertical" (│).

How can I make the Python Launcher use my default Python version from pyenv?

If you're using pyenv to manage your Python versions, you'll want to set the version the Launcher uses to the pyenv global version.

Add this line to your .zshrc or .bashrc file:

export PY_PYTHON=$(pyenv exec python -c "import sys; print('.'.join(map(str, sys.version_info[:2])))")

Or this line to your ~/.config/fish/config.fish file:

set -gx PY_PYTHON (pyenv exec python -c "import sys; print('.'.join(map(str, sys.version_info[:2])))")

Appendix

• PEP 397: Python launcher for Windows
• PEP 486: Make the Python Launcher aware of virtual environments
• Python Launcher for Windows
  • Documentation
  • Source