Managing Python Versions Effectively

After recently upgrading my homebrew, links to python2 and pip2 broke! I had no way to run different versions of Python. This left me searching for a more effective way to manage Python versions and dependencies.

I discovered pyenv, a great tool for specifying exact Python versions. It also integrates nicely with virtual environments and Jupyter!

Setting Up Pyenv

  1. Install pyven
    brew install pyenv
  2. Setup .bash_profile to configure and initialize pyenv
    # pyenv for running specific python version
    export PYENV_ROOT="$HOME/.pyenv"
    export PATH="$PYENV_ROOT/bin:$PATH"
    # initialize pyenv and virtualenv in shell
    if command -v pyenv 1>/dev/null 2>&1; then  
    eval "$(pyenv init -)"
    eval "$(pyenv virtualenv-init -)"
    # show virtualenv changes in prompt

Using Pyenv

  • Install a specific python version
    $ pyenv install 2.7.10
    $ pyenv install 3.5.0
    $ pyenv versions

You can similarly uninstall a specific version using uninstall.

pyenv introduces three scopes for using python versions. It uses the first found in order of specificity: shell, local, and global (else defaults to system python).

  • Set the global Python version
    $ pyenv global 2.7.10
  • Set the local version
    $ pyenv local 3.10
    # to remove
    $ pyenv local --unset 

    This creates a .python-version file in the directory. Pyenv automatically activates the local python version for all subdirectories:

  • Shell overrides the python version for this shell session
    $ pyenv shell 2.7.10
    $ pyenv shell --unset

Virtual Environments

Install virtualenv plugin for pyenv.

Use Homebrew: brew install pyenv-virtualenv

Working with Virtual Environments

  • Create a new virtual environment
    $ pyenv virtualenv 2.7.10 my-project-2.7.10

This stores the virtualenv in a new directory my-project-2.7.10 under $(pyenv root)/versions/—similar to virtualenvwrapper.

  • Activate or deactivate
    $ pyenv activate <name>
    $ pyenv deactivate

Pyenv and Jupyter

How do you setup Jupyter kernels for Python 2 and Python 3?

  1. activate shell for each python version pyenv activate 2.7.14
  2. Install Jupyter pip install jupyter
  3. Install Kernel python -m ipykernel install --user

Et voila!