Update self to include only the difference with other.

def difference_update(self, other):
		"""Update self to include only the difference with other."""
		other = set(other)
		indices_to_delete = set()
		for i, elem in enumerate(self):
			if elem in other:
				indices_to_delete.add(i)
		if indices_to_delete:
			self._delete_values_by_index(indices_to_delete)