Parse jstring and return a Python data structure.

        'jstring' a string of JSON. May not be None.

        Returns a Python data structure.

        If jstring couldn't be parsed, raises an APIDataException.

def _parse_json(self, jstring=None):
        """Parse jstring and return a Python data structure.

        'jstring' a string of JSON. May not be None.

        Returns a Python data structure.

        If jstring couldn't be parsed, raises an APIDataException."""

        # Argument error checking.
        assert jstring is not None

        result = None

        try:
            result = json.loads(jstring)
        except (ValueError) as exception:
            msg = 'Unable to convert JSON string to Python data structure.'
            raise APIDataException(exception, jstring, msg)

        return result