Autoload virtualenv from .venv when moving into a directory

.zshrc

# autoload venv if there's a .venv file
# Support for bash
PROMPT_COMMAND='prompt'

# Mirrored support for zsh. See: https://superuser.com/questions/735660/whats-the-zsh-equivalent-of-bashs-prompt-command/735969#735969 
precmd() { eval "$PROMPT_COMMAND" }

function prompt()
{
    if [ "$PWD" != "$MYOLDPWD" ]; then
        MYOLDPWD="$PWD"
        test -e .venv && workon `cat .venv`
        test -e .venv || deactivate &> /dev/null
    fi
}