from starlette.routing import Mount


def mount_if_not_exists(app, path: str, sub_app):
  """
  Mounts a sub-application only if no Mount object already exists
  at the specified path in the main application's router.
  """
  is_mounted = False
  
  for route in app.router.routes:
    
    if isinstance(route, Mount):
      if route.path == path:
        is_mounted = True
        break
  
  if not is_mounted:
    app.mount(path, app=sub_app)