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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_path_str(self, sep=os.path.sep, type_str=None):
 """Get path from root to this node. Args: sep: str One or more characters to insert between each element in the path. Defaults to "/" on Unix and "\" on Windows. type_str: SUBJECT_NODE_TAG, TYPE_NODE_TAG or None. If set, only include information from nodes of that type. Returns: str: String describing the path from the root to this node. """

        return sep.join(
            list(
                reversed(
                    [
                        v.label_str
                        for v in self.parent_gen
                        if type_str in (None, v.type_str)
                    ]
                )
            )
        )