How to use the pyleri.node.Node function in pyleri

Returns a nodeResult with the following attributes:
         - is_valid: True when the string is successfully parsed
                     by the Grammar.
         - pos: position in the string where parsing ended.
                (this is the end of the string when is_valid is True)
         - expecting: a list containing possible elements at position
                      'pos' in the string.
         - tree: the parse_tree containing a structured
                 result for the given string.
        '''
        self._string = string
        self._expecting = Expecting()
        self._cached_kw_match.clear()
        self._len_string = len(string)
        self._pos = None
        tree = Node(self._element, string, 0, self._len_string)
        node_res = Result(*self._walk(
            self._element,
            0,
            tree.children,
            self._element,
            True))

        # get rest if anything
        rest = self._string[node_res.pos:].lstrip()

        # set is_valid to False if we have 'rest' left.
        if node_res.is_valid and rest:
            node_res.is_valid = False

        # add end_of_statement to expecting if this is possible
        if not self._expecting.required and rest:

def _walk(self, element, pos, tree, rule, is_required):
        if self._pos != pos:
            self._s = self._string[pos:].lstrip()
            self._pos = self._len_string - len(self._s)
        node = Node(element, self._string, self._pos)
        self._expecting.set_mode_required(node.start, is_required)

        return element._get_node_result(self, tree, rule, self._s, node)

def _walk(self, element, pos, tree, rule, is_required):
        if self._pos != pos:
            self._s = self._string[pos:] #.lstrip() # don't strip whitespace
            self._pos = self._len_string - len(self._s)
        node = Node(element, self._string, self._pos)
        self._expecting.set_mode_required(node.start, is_required)
        return element._get_node_result(self, tree, rule, self._s, node)