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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 _load_cwr_defaults(self):
 """ Loads the CWR default values file, creating a matrix from it, and then returns this data. The file will only be loaded once. :return: the CWR default values matrix """

        if self._cwr_defaults is None:
            self._cwr_defaults = self._reader.read_yaml_file(
                self._file_defaults)

        return self._cwr_defaults