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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 save_dot(self, file_name='graph.dot'):
 """Save the graph in a graphviz dot file. Parameters file_name : Optional[str] The name of the file to save the graph dot string to. """

        s = self.get_string()
        with open(file_name, 'wt') as fh:
            fh.write(s)