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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 add(self, layer, items):
 """ Add items in model. """

        for k in items.iterkeys():
            if k in self.model[layer]:
                raise Exception('item %s is already in layer %s' % (k, layer))
        self.model[layer].update(items)
        # this should also update Layer.layer, the layer data
        # same as calling layer constructor
        # so now just need to add items to the layer
        for k, v in items.iteritems():
            getattr(self, layer).add(k, v['module'], v.get('package'))