<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get(self, identifier, default=None):
 """Get a node of the AttrTree using its path string. Args: identifier: Path string of the node to return default: Value to return if no node is found Returns: The indexed node of the AttrTree """

        split_label = (tuple(identifier.split('.'))
                       if isinstance(identifier, str) else tuple(identifier))
        if len(split_label) == 1:
            identifier = split_label[0]
            return self.__dict__.get(identifier, default)
        path_item = self
        for identifier in split_label:
            if path_item == default or path_item is None:
                return default
            path_item = path_item.get(identifier, default)
        return path_item