Normally when you run the shell script to activate your virtual environment, it sets the VIRTUAL_ENV environment variable and prepends the bin/ directory to PATH . I also tossed in IN_VIRTUAL_ENV and DEFAULT_ENV_DIR constants to detect when you're running from a virtual environment and the default name to use when creating a virtual environment, respectively. We did this because we regularly found beginners committing their virtual environments to source control without realizing that virtual environments are not portable between machines.