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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 _enforceDataType(self, data):
 """ Converts to int so that this CTI always stores that type. The data be set to a negative value, e.g. use -1 to select the last item by default. However, it will be converted to a positive by this method. """

        idx = int(data)
        if idx < 0:
            idx += len(self._displayValues)
        assert 0 <= idx < len(self._displayValues), \
            "Index should be >= 0 and < {}. Got {}".format(len(self._displayValues), idx)
        return idx