The Python Launcher for Unix
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. By having a command that is
version-agnostic command 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.
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.
For instructions on how to use the Python Launcher, see the top section of
py --help
.
Installation
You can either install from crates.io or from source. Both approaches require you install the Rust toolchain. You can use rustup to accomplish this or whatever your OS suggests.
If you want to install from crates.io, run:
cargo install python-launcher
If you want to install from source, run:
cargo install --path .
Search order
Please note that while searching, the search for a Python version can become more specific. This leads to a switch in the search algorithm to the one most appropriate to the specificity of the version.
You can always run the Python Launcher with PYLAUNCH_DEBUG
set to some value
to have it output logging details of how it is performing its search.
py -3.6
(specific version)
- Search
PATH
forpython3.6
py -3
(loose/major version)
- Check for the
PY_PYTHON3
environment variable, and if defined and not the empty string then use it as the specific version (e.g.PY_PYTHON3=3.6
) - Search
PATH
for all instances ofpython3.*
- Find the executable with the newest version number that comes earliest on
PATH
py
(any version)
- Use
${VIRTUAL_ENV}/bin/python
immediately if available - Use
.venv/bin/python
if available in the current working directory or any of its parent directories - If the first argument is a file path ...
- Check for a shebang
- If shebang path starts with
/usr/bin/python
,/usr/local/bin/python
,/usr/bin/env python
orpython
, proceed based on the version found on that path (barepython
is considered the equivalent of not specifying a Python version)
- Check for the
PY_PYTHON
environment variable, and if defined then use it as the loose or specific version (e.g.PY_PYTHON=3
orPY_PYTHON=3.6
) - Search
PATH
for all instances ofpython*.*
- Find the executable with the newest version that is earliest on
PATH