Installing Python

Although, at time of writing, Python 2.x is still to be found as the default python install on many systems, it is no longer maintained since January of 2020. Python 3.x has some distinct differences so unless you specifically want to test your code in 2.x, make sure you have access to Python 3.x. You can confirm your version with python --version.

There are multiple ways to manage your Python versions. This guide looks at just one of them.

Installing pyenv / pyenv-win

On MacOS and Linux

pyenv is a great option for installing multiple versions and being able to switch between them.

• Install pyenv via homebrew: brew install pyenv (it's optional, but recommended to also brew install openssl readline sqlite3 xz zlib)
• Add pyenv init to your shell:
  • echo -e 'if command -v pyenv 1>/dev/null 2>&1; then\n eval "$(pyenv init -)"\nfi' >> ~/.<your-shell-config-file>
  • Your shell config file may be .zshrc, .bash_profile, .bashrc
  • If you are not sure, cd ~, ls -lah and see which one is there!

On Windows

There is a pyenv-win port.

• Install pyenv via Chocolatey: choco install pyenv-win (Do not install pyenv via your administrative shell as this will not give you access as a local user)
• Close and reopen your terminal app and run pyenv --version
  • If you receive a permission denied or a command not found error, check the documentation for how to manually set environment variables even if you used Chocolatey.
• Navigate to your home directory and run pyenv rehash

Basic pyenv / pyenv-win usage

On MacOS and Linux

• Install a Python version with pyenv: pyenv install <latest-version> (use pyenv install -l to see all the options, you will need to replace <latest-version> with the actual latest version eg. 3.9.1!)
• See your installed Python version: pyenv versions
• Switch to a version: pyenv global <version> eg. pyenv global 3.9.1
• Close and reopen your terminal app.
• Confirm success by running python --version

On Windows

• Install a Python version with pyenv: pyenv install <latest-version> (use pyenv install -l to see all the options. If you do not see all the versions of Python you are expecting you may need to run pyenv update. You will need to replace <latest-version> with the actual latest version eg. 3.9.1!).
• See your installed Python version: pyenv versions
• Switch to a version: pyenv global <version> eg. pyenv global 3.9.1
• Run pyenv rehash to update pyenv with your new settings.
• Confirm success by running python --version

Note:

• If you are running Windows 10 1905 or newer, you made need to disable the built-in Python launcher via Start > "Manage App Execution Aliases" and disabling the "App Installer" aliases for Python.
• Failing that you may have to alter your environment variables so that any pyenv paths are higher in the list, and therefore take precedence over any other Python paths, including other Python package managers such as Anaconda. (Remember to restart your machine for changes to take effect.)
• As a last resort you might have to uninstall Python before pyenv will work.