code: def update(self, items):
          
          for parent, sub_items in _iterate_dependencies(items):
              for si in sub_items:
                  dep = self._deps[si]
                  if parent not in dep.parent:
                      dep.parent.append(parent)
docs: Updates the dependencies in the inverse relationship format, i.e. from an iterable or dict that is structured
          as `(item, dependent_items)`. The parent element `item` may occur multiple times.
  
          :param items: Iterable or dictionary in the format `(item, dependent_items)`.
          :type items: collections.Iterable