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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_model(self, file_name='model.sbgn'):
 """Save the assembled SBGN model in a file. Parameters file_name : Optional[str] The name of the file to save the SBGN network to. Default: model.sbgn """

        model = self.print_model()
        with open(file_name, 'wb') as fh:
            fh.write(model)