How to use the jupyterlab.jupyterlab.jlpmapp.HERE.startswith function in jupyterlab

def get_app_dir():
    """Get the configured JupyterLab app directory.
    """
    # Default to the override environment variable.
    if os.environ.get('JUPYTERLAB_DIR'):
        return osp.realpath(os.environ['JUPYTERLAB_DIR'])

    # Use the default locations for data_files.
    app_dir = pjoin(sys.prefix, 'share', 'jupyter', 'lab')

    # Check for a user level install.
    # Ensure that USER_BASE is defined
    if hasattr(site, 'getuserbase'):
        site.getuserbase()
    userbase = getattr(site, 'USER_BASE', None)
    if HERE.startswith(userbase) and not app_dir.startswith(userbase):
        app_dir = pjoin(userbase, 'share', 'jupyter', 'lab')

    # Check for a system install in '/usr/local/share'.
    elif (sys.prefix.startswith('/usr') and not
          osp.exists(app_dir) and
          osp.exists('/usr/local/share/jupyter/lab')):
        app_dir = '/usr/local/share/jupyter/lab'

    return osp.realpath(app_dir)