def has_unique_forward_path(self, start_dataframe_name, end_dataframe_name):
        """
        Is the forward path from start to end unique?

        This will raise if there is no such path.
        """
        paths = self.find_forward_paths(start_dataframe_name, end_dataframe_name)

        next(paths)
        second_path = next(paths, None)

        return not second_path

        Is the forward path from start to end unique?

        This will raise if there is no such path.
        
featuretools/entityset/entityset.py