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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.cx'):
 """Save the assembled CX network in a file. Parameters file_name : Optional[str] The name of the file to save the CX network to. Default: model.cx """

        with open(file_name, 'wt') as fh:
            cx_str = self.print_cx()
            fh.write(cx_str)