Virtual environments and embedding Python

The virtualenv documentation includes a Using virtualenv without bin/python section that hints at how to configure a virtual environment once the interpreter is already running.

To avoid hardcoding the path to the activate_this.py script, I use the following snippet:

def resolve_virtual_environment(override=None): """Fetch the virtual environment path in the process' environment or use an override.""" path = os.getenv('VIRTUAL_ENV') if override: path = os.path.join(os.getcwd(), override) return path def activate_virtual_environment(environment_root): """Configures the virtual environment starting at ``environment_root``.""" activate_script = os.path.join( environment_root, 'Scripts', 'activate_this.py') execfile(activate_script, {'__file__': activate_script}) 

And you can use it like so:

if __name__ == '__main__': # use first argument is provided. override = None if len(sys.argv) > 1: override = sys.argv[1] environment_root = resolve_virtual_environment(override) 

You can fetch the override value from a configuration file or something instead of from the command-line argument.

Note that you can only still use a single virtual environment pre-process.

Note: in contrast with using the interpreter bundled in the virtual environment, you have access to the packages installed for the interpreter you started. For example, when using a globally-installed Python, you will have access to the globally-installed packages.

Also make sure that you use a Python interpreter with a version that matches whatever version you used to create the virtual environment to make sure that the standard library (copied into the virtual environment) version matches the Python interpreter version.