code: def suggest_path(root_dir):
      
      if not root_dir:
          return [os.path.abspath(os.sep), '~', os.curdir, os.pardir]
  
      if '~' in root_dir:
          root_dir = os.path.expanduser(root_dir)
  
      if not os.path.exists(root_dir):
          root_dir, _ = os.path.split(root_dir)
  
      return list_path(root_dir)
docs: List all files and subdirectories in a directory.
      If the directory is not specified, suggest root directory,
      user directory, current and parent directory.
      :param root_dir: string: directory to list
      :return: list