The Python Launcher for UNIX

An implementation of the py command for UNIX-based platforms.

The goal is to have py become the cross-platform command that all Python users use when executing a Python interpreter. By having a version-agnostic command 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 is installed). This also unifies the suggested command to document for launching Python on both Windows as UNIX as py which has existed as the preferred command on Windows for some time.

See the top of py --help for instructions.

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.

py -3.6 (specific version)

  1. Search PATH for python3.6

py -3 (loose/major version)

  1. Use the version found in the PY_PYTHON3 environment variable if defined (e.g. PY_PYTHON3=3.6)
  2. Search PATH for all instances of python3.Y
  3. Find the executable with largest Y

py (any/unknown version)

  1. If the first argument is a file path ...
    1. Check for a shebang
    2. If executable starts with /usr/bin/python, /usr/local/bin/python, /usr/bin/env python or python, proceed based on the version found (bare python is considered python2 for backwards-compatibility)
  2. Use ${VIRTUAL_ENV}/bin/python immediately if available
  3. Use the version found in the PY_PYTHON environment variable if defined (e.g. PY_PYTHON=3 or PY_PYTHON=3.6)
  4. Search PATH for all instances of pythonX.Y
  5. Find the executable with the largest X.Y

TODO

NOTE: I am using this project to learn Rust, so please don't be offended if I choose to implement something myself instead of accepting a pull request that you submit. (Pull requests to do something I have already implemented in a more idiomatic fashion are very much appreciated, though.)

PEP 397: Python launcher for Windows (documentation)