How to use the asttokens.mark_tokens.MarkTokens function in asttokens

def mark_tokens(self, root_node):
    """
    Given the root of the AST or Astroid tree produced from source_text, visits all nodes marking
    them with token and position information by adding ``.first_token`` and
    ``.last_token``attributes. This is done automatically in the constructor when ``parse`` or
    ``tree`` arguments are set, but may be used manually with a separate AST or Astroid tree.
    """
    # The hard work of this class is done by MarkTokens
    MarkTokens(self).visit_tree(root_node)