Find Python installed by python.org macOS installers

[uranusjr]

python.org installers for macOS install Python to /Library/Frameworks/Python.framework/Versions/X.Y (replace X.Y with actual versions), but the installed binary is not always linked into PATH. It would be useful to find Python binaries inside it automatically.

The binaries are at /Library/Frameworks/Python.framework/Versions/X.Y/bin/pythonX.Y (pythonX.Ym is also available).