Auto-enter Python virtual environment.

auto-enter-py-virtualenv.sh

# Finds a Python virtual environment in the current
# directory or any of its parents and enters it, or
# exits an virtual environment if we're in one
# but the current directory does not contain a virtualenv
function find_and_enter_virtualenv {
    # See if the current directory, or any of its
    # parents have a 'env/bin/activate' script
    path=$(pwd)
    while [ ! -z $path ]; do
        if [ -f "$path/env/bin/activate" ]; then
            path="$path/env/bin/activate"
            break
        fi

        path="${path%/*}"
    done

    # No virtualenv found, try to de-activate
    # in case we're exiting one
    if [ -z $path ]; then
        deactivate &> /dev/null
        return
    fi

    # Enter the virtualenv
    source $path
}

# Override `cd` so we can intercept directory changes
function cd {
    builtin cd "$@"
    find_and_enter_virtualenv
}

# Suppose a bash prompt is opened and that directory
# is a virtual env, we'll activate it!
find_and_enter_virtualenv