A datastructure, first described by Huet, is used to traverse and manipulate immutable trees. This library is a port of the zipper implementation found in Clojure.
The zipper module provides several functions for creating a Loc object which represents the current focal point in the tree.
>>> import zipper
>>> top = zipper.list([1, [2, 3], 4])
>>> print top.down().right().node()
[2,3]
>>> print top.down().right().down().node()
2
>>> print top.down().right().down().replace(0).root()
[1, [0, 3], 4]