Where do I find Python?

In order to see /usr/local/bin in Finder you might want to press Cmd+Shift+G while in Finder, type /usr/local/bin and click Go.

There are some fundamental differences between Python 2 and Python 3, such that both keep being developed side-by-side. P3 is not the successor to P2 like other software versions.

Latest Python 3 Release - Python 3.6.5 (2018-03-28)

Latest Python 2 Release - Python 2.7.14 (2017-09-16)

In development Python 3.7.0b3 (2018-03-29)

In development Python 2.7.15rc1 (2018-04-15)

Python documentation

Never remove, and/or replace the System installed python as several operating system components depend on this specific 2.7.10 version of Python. Use a package manager (e.g. homebrew), or install from the python.org installer to keep the python versions separate. The python installed by the operating system is /usr/bin/python.

Assuming that you have the proper (default) PATH environment variable setting, then you should be able to just type the following (in blue) from the Terminal command-line:

# launch the default python 2.7.10 interactive development environment (IDE)

$ idle &

$ python -c 'print("{}".format("Monty Python"))'

You use control-d to exit the idle utility. Note: I launch idle as a Bash background (&) task to free up the Terminal.

The alternate python installation choices usually put the python and idle binaries in /usr/local/bin, and shove the respective python version library into (for example, Python 3.6.5) at the following location:

/Library/Frameworks/Python.framework/Versions/3.6/lib

With the System python installation, the environment variable PYTHONPATH is unset. This, and other environment variables are discussed in the python documentation at python.org. But, when you install different Python versions (e.g. above), you must set this environment variable as the path to the specific Python version library. So as above, if you wanted to run the Python 3.6.5 that you installed with python.org's installer, you set the path to the dynamic framework library as:

$ export PYTHONPATH=/Library/Frameworks/Python.framework/Versions/3.6/lib

and then you could launch Python 3.6.5, or idle3 as:

$ python3

$ idle3 &

When you are done, and want to run the operating system python again, you unset the PYTHONPATH environment variable as:

$ unset PYTHONPATH

There are enough language version differences between python 2.7.14 and python 3.6.5 (presently) that depending on the particular library module used, that code that you write for python 2.7.n will not work with python 3.6.n without some planning. Some python 3 features have been back ported to python 2.

Python is not a GUI tool, and is not launchable/configurable from the Finder. Python is a scripting language, and by that very nature, it is intended to be used from the Terminal command-line, not Finder.

Once in the Terminal, you will automatically have /usr/local/bin and /usr/bin in your default PATH, and you can access Python from the Terminal command-line as I described in my previous post.