Freeze your python pip requirements to a known place, to guard against Homebrew mess-ups

freezenv.sh

freezenv() {
    FUNCDESC='Freeze the active Python Environment pip requirements.

This stores the requirements.txt in the active $VIRTUAL_ENV or $CONDA_PREFIX
directory, overwriting any existing requirements file.'

    if [[ -z ${VIRTUAL_ENV-$CONDA_PREFIX} ]] ; then
        error "$FUNCNAME: no active python or conda venv"
        return 1
    fi
    local VENV_REQS=${VIRTUAL_ENV-$CONDA_PREFIX}/requirements.txt
    echo "Storing PIP package list into ${VENV_REQS}"
    pip freeze > ${VENV_REQS}
}

• Replace error with echo if you don't have an error function that writes to STDERR

Why? Because whenever you update python in Homebrew on a Mac, it makes a mess of your existing python virtual environments that link to libraries and executables that no longer exist. So you have to re-create the virtual environment.

Only because it's broken, you can't activate the venv to do a pip freeze after the fact.

So, whenever you add a package in a venv with pip install somepackage you should then freezenv to keep a record of the installed packages.

Probably I should make another function to install-and-freeze in one go...

not really necessary for Anaconda, since Homebrew won't mess with that. But I include the functionality for conda too, in case it's needed for other reasons.