code: def _get_file_key(self, file_path, link_path):
          
          if os.path.isabs(link_path):
              return link_path
          else:
              file_dir = os.path.dirname(file_path)
              joined_path = os.path.join(file_dir, link_path)
              return os.path.abspath(joined_path)
docs: Finds the absolute path of link_path relative to file_path. The
          absolute path is the key to anchors dictionary used throughout the
          AnchorHub process
  
          :param file_path: string file path of the file that contains the link
              being examined
          :param link_path: string. The link URL that we'd like to find the
              absolute path for
          :return: the absolute path of link_path relative to file_path