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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, fname='model.js'):
 """Save the assembled Cytoscape JS network in a js file. Parameters file_name : Optional[str] The name of the file to save the Cytoscape JS network to. Default: model.js """

        exp_colorscale_str = json.dumps(self._exp_colorscale)
        mut_colorscale_str = json.dumps(self._mut_colorscale)
        cyjs_dict = {'edges': self._edges, 'nodes': self._nodes}
        model_str = json.dumps(cyjs_dict, indent=1, sort_keys=True)
        model_dict = {'exp_colorscale_str': exp_colorscale_str,
                      'mut_colorscale_str': mut_colorscale_str,
                      'model_elements_str': model_str}
        s = ''
        s += 'var exp_colorscale = %s;\n' % model_dict['exp_colorscale_str']
        s += 'var mut_colorscale = %s;\n' % model_dict['mut_colorscale_str']
        s += 'var model_elements = %s;\n' % model_dict['model_elements_str']
        with open(fname, 'wb') as fh:
            fh.write(s.encode('utf-8'))