The relative path (from environment root) to python.

def _python_rpath(self):
        """The relative path (from environment root) to python."""
        # Windows virtualenv installation installs pip to the [Ss]cripts
        # folder. Here's a simple check to support:
        if sys.platform == 'win32':
            return os.path.join('Scripts', 'python.exe')
        return os.path.join('bin', 'python')