How to setup python on Mac Systsem

I’ve been dipping my toe back into Python development as I get ready to head to PyCon US. (If you’re headed there as well and want to share your Python story, let me know!) When I installed a module to tinker around with, I got a reminder that I needed to install Python 3 soon.

$ pip install todoist-python DEPRECATION: Python 2.7 will reach the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 won’t be maintained after that date. A future version of pip will drop support for Python 2.7.

So, I did what any of us would do and googled around looking for a guide to update my development environment, which runs on Mac (the macOS operating system, formerly known as OS X). To my surprise, I found only a handful of StackOverflow posts, and they pointed me to partial solutions. Here’s the full story of how to set up your environment without breaking anything built into the macOS operating system.

1. Install pyenv

Moshe Zadka cautions that doing this wrong could result in an unreliable idea of which Python is running that depends too closely on shells loading aliases. I knew Moshe was familiar with Python, but what I didn’t know is that he is an author of many Python tutorials as well as an upcoming book on Python development on macOS. He helped 40 colleagues develop Python safely and consistently on macOS systems following one core principle:

“The basic premise of all Python development is to never use the system Python. You do not want the Mac OS X ‘default Python’ to be ‘python3.’ You want to never care about default Python.”

How do we stop caring about the default? Moshe recommends using pyenv to manage Python environments (for a deeper dive on configuring pyenv, see this article). This tool manages multiple versions of Python and is described as “simple, unobtrusive, and follows the Unix tradition of single-purpose tools that do one thing well.”

While other installation options are available, the easiest way to get started is with Homebrew:

$ brew install pyenv ? /usr/local/Cellar/pyenv/1.2.10: 634 files, 2.4MB

Install Python

Now let’s install the latest Python version (3.7.3 as of this writing):

    $ pyenv install 3.7.3
    python-build: use openssl 1.0 from homebrew
    python-build: use readline from homebrew
    Downloading Python-3.7.3.tar.xz...
    -> https://www.python.org/ftp/python/3.7.3/Python-3.7.3.tar.xz
    Installing Python-3.7.3...
    ## further output not included ##

Set your global default

Now that Python 3 is installed through pyenv, we want to set it as our global default version for pyenv environments:

    $ pyenv global 3.7.3
    # and verify it worked 
    $ pyenv version
    3.7.3 (set by /Users/mbbroberg/.pyenv/version)

The power of pyenv comes from its control over our shell’s path. In order for it to work correctly, we need to add the following to our configuration file (.zshrc for me, possibly .bash_profile for you):

    $ echo -e 'if command -v pyenv 1>/dev/null 2>&1; thenn  eval "$(pyenv init -)"nfi' >> ~/.zshrc

After that command, our dotfile (.zshrc for zsh or .bash_profile for Bash) should include these lines:

    if command -v pyenv 1>/dev/null 2>&1; then
      eval "$(pyenv init -)"
    fi

Now we know for certain that we’re using Python 3.7.3 and pip will update alongside it without any manual aliasing between versions. Using Moshe’s recommendation to use a version manager (pyenv) enables us to easily accept future upgrades without getting confused about which Python we are running at a given time.

Success

As you get comfortable with this workflow, you can [use pyenv to manage multiple versions of Python