def __set__(self, instance, value):
recipe_categories = instance.xml.xpath('./head/recipe_categories')
if len(recipe_categories) != 0:
instance.xml.head.remove(recipe_categories[0])
value = self._remove_duplicates(value)
if len(value) > 0:
el = E.recipe_categories()
for item in value:
el.append(E.category(code=item.code))
instance.xml.head.append(el)
