code: def _write_config_file(self, config_data, indent=2):
          
          with open(self.config, 'w') as f:
              json.dump(config_data, f, indent=indent)
docs: write config data to file.
  
             Parameters
             ==========
             config_data: the Configuration object to save a username and
                          password, if defined
             indent: number of tab indentations to use when writing json