def _ComputeDeltas(old_items, new_items):
  """Finds the added and removed items in a new set compared to an old one.

  Args:
    old_items: A collection of existing items. Could be a list or set.
    new_items: Another collection of items.

  Returns:
    A pair of sets (added, removed).
  """
  old, new = set(old_items), set(new_items)
  return new - old, old - new