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How to set Python's default version to 3.x on OS X?

On macOS, you may already have multiple Python versions installed (e.g., the system’s default Python 2.7 and a newer Python 3.x). If you want the command python to run Python 3 by default, there are several approaches. Below are some commonly used methods:

1. Create an Alias

The simplest way to default to Python 3 in your personal shell sessions is to set an alias in your shell configuration file (e.g., ~/.zshrc or ~/.bashrc). For Zsh (the default shell on newer macOS versions):

# In your ~/.zshrc
alias python="python3"

After saving the file, reload your shell:

source ~/.zshrc

Now when you type python in a new terminal session, it will run Python 3.

Pros:

  • Very simple and reversible.
  • Doesn’t affect system-wide scripts.

Cons:

  • Applies only to your user account and only when using a shell that reads your config file (Zsh, Bash, etc.).

2. Adjust Your PATH (Homebrew Installation)

If you install Python 3 via Homebrew, it typically places the Python 3 binary in /usr/local/bin (for Intel Macs) or /opt/homebrew/bin (for Apple Silicon Macs), named python3. You can adjust your PATH so that a symlink named python points to the Python 3 binary.

  1. Install Python 3 via Homebrew (if you haven’t already):

    brew update
brew install python

    (This installs the latest Python 3, usually as python3.)

  2. Check where Homebrew installed Python:

    which python3
# Typically /usr/local/bin/python3 or /opt/homebrew/bin/python3

  3. Create a symlink named python (optional step if you want the command python to point to Python 3 system-wide):

    ln -s /usr/local/bin/python3 /usr/local/bin/python

    or, for Apple Silicon:

    ln -s /opt/homebrew/bin/python3 /opt/homebrew/bin/python

  4. Ensure /usr/local/bin or /opt/homebrew/bin is at the front of your PATH in your shell config file (e.g., ~/.zshrc or ~/.bashrc):

    export PATH="/usr/local/bin:$PATH"

    or, for Apple Silicon:

    export PATH="/opt/homebrew/bin:$PATH"

Now, when you type python in a new terminal, it should invoke Python 3.

Pros:

  • Makes Python 3 available system-wide as python.
  • Straightforward for Homebrew-based workflows.

Cons:

  • Changing system-wide defaults can create conflicts with scripts expecting Python 2 (though modern macOS no longer includes Python 2 by default, many older scripts still assume python is Python 2).
  • Requires you to maintain your symlinks if you install/update multiple Python versions.

3. Use pyenv for Version Management

If you need more flexibility (e.g., different Python versions for different projects), consider using pyenv. It lets you install and switch between Python versions seamlessly.

  1. Install pyenv (via Homebrew or manual setup):

    brew install pyenv

  2. Configure your shell (add these lines to ~/.zshrc or ~/.bashrc):

    export PYENV_ROOT="$HOME/.pyenv"
export PATH="$PYENV_ROOT/bin:$PATH"
eval "$(pyenv init -)"

  3. Install and set a global Python 3 version:

    pyenv install 3.11.2
pyenv global 3.11.2

  4. Verify:

    python --version
# Should show Python 3.11.2 (or whichever version you installed)

Pros:

  • Easily manage multiple Python versions.
  • Allows per-project or global defaults.
  • Minimizes the risk of breaking system scripts.

Cons:

  • Slightly more involved setup.
  • Must remember to use pyenv commands to manage versions.

Important Note About System Python

macOS used to ship with Python 2 in /usr/bin/python and Python 3 in /usr/bin/python3. As of macOS 12 (Monterey) and later, Apple no longer includes Python 2 by default. If you are on an older macOS version, be aware that replacing or altering the system Python can break system scripts or tools that rely on Python 2. It’s best practice to leave Apple’s Python alone and install your own version(s) of Python in /usr/local/ or /opt/homebrew/, then adjust your environment accordingly.

Level Up Your Python Skills

Once you’ve set up Python 3 as your default, you may want to enhance your Python knowledge further. Consider these resources from DesignGurus.io:

And if you’re aiming to land a role at a major tech company, you’ll often need system design expertise. For that:

Don’t forget the DesignGurus YouTube Channel for free video resources on both coding and system design topics.

Final Thoughts

Switching your default Python on macOS to Python 3 can be done in multiple ways, from adding a simple alias to using dedicated tools like pyenv. The best approach depends on how deeply you want to customize your environment, whether you’re managing multiple Python versions, and how comfortable you are with system-level changes. In any case, be cautious with the system Python that ships with macOS—avoid overwriting it and rely on user-level or Homebrew installations to keep everything working smoothly.

Happy Coding!

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