This might have been unintentional, but I suspect "Spectre of Structure" and "Python's missing piece" refer to Nathan Marz's specter library for clojure [1], similarly touted as clojure's missing piece. I tend to agree in the case of specter, given the mind-boggling types of transformations that are easily (and simply) expressed in it (and often run faster than idiomatic clojure as well). Highly recommended if you ever need to work with deeply nested data structures.
[1] https://github.com/nathanmarz/specter