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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 setup_params(self, data):
 """ Verify, modify & return a copy of the params. """

        # Variable for which to do the stacking
        if 'ymax' in data:
            if any((data['ymin'] != 0) & (data['ymax'] != 0)):
                warn("Stacking not well defined when not "
                     "anchored on the axis.", PlotnineWarning)
            var = 'ymax'
        elif 'y' in data:
            var = 'y'
        else:
            warn("Stacking requires either ymin & ymax or y "
                 "aesthetics. Maybe you want position = 'identity'?",
                 PlotnineWarning)
            var = None

        params = self.params.copy()
        params['var'] = var
        params['fill'] = self.fill
        return params