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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 update(self, items):
 """ Updates the dependencies with the given items. Note that this does not reset all previously-evaluated and cached nodes. :param items: Iterable or dictionary in the format `(dependent_item, dependencies)`. :type items: collections.Iterable """

        for item, parents in _iterate_dependencies(items):
            dep = self._deps[item]
            merge_list(dep.parent, parents)