Installing pyenv

Why

It can be helpful to install Firedrake using a Python executable installed with pyenv rather than a system provided version. This is because:

• When the system Python bumps a minor version (e.g. 3.10 -> 3.11) the Firedrake virtual environment will still work.
• MacOS ships with a broken Python installation and the homebrew version also does not always work.

How

To install pyenv (assuming MacOS with homebrew installed) one needs to:

1. Install build dependencies
2. Install pyenv

   brew install pyenv
   

3. Set PYENV_ROOT and PATH

   $ export PYENV_ROOT=$HOME/.pyenv
   $ export PATH=$PYENV_ROOT/bin:$PATH
   

4. Initialise the shell

   $ eval "$(pyenv init -)"
   

   Note that this command is optional. One can instead find the installed Python versions under $(pyenv root)/versions. See here for more information.
5. Install a Python version (here 3.11)

   $ pyenv install 3.11
   

6. Set this Python as the default for this shell (only if using pyenv init)

   $ pyenv shell 3.11
   

7. Run firedrake-install, python will resolve to the correct executable

   $ python firedrake-install <args>
   

Note that the above instructions are equivalent to those found here.