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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 _get_agg_axis(self, axis_num):
 """ Let's be explicit about this. """

        if axis_num == 0:
            return self.columns
        elif axis_num == 1:
            return self.index
        else:
            raise ValueError('Axis must be 0 or 1 (got %r)' % axis_num)