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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_pdf(self, file_name='graph.pdf', prog='dot'):
 """Draw the graph and save as an image or pdf file. Parameters file_name : Optional[str] The name of the file to save the graph as. Default: graph.pdf prog : Optional[str] The graphviz program to use for graph layout. Default: dot """

        self.graph.draw(file_name, prog=prog)