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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_label_set(self, type_str=None):
 """Get a set of label_str for the tree rooted at this node. Args: type_str: SUBJECT_NODE_TAG, TYPE_NODE_TAG or None. If set, only include information from nodes of that type. Returns: set: The labels of the nodes leading up to this node from the root. """

        return {v.label_str for v in self.node_gen if type_str in (None, v.type_str)}