Comment by Permik

Yeah, by implicit ordering, I mean an underspecified pipeline which has an undeclared dependency on some of the inputs being sorted. Unfortunately this is why the code in the cited paper worked on some systems and not others as the os.listdir() call didn't guarantee sorted results and thus the assumed invariants were broken.

Requiring code to be explicit about its invariants by default is just plain good design and makes things more robust. And when being more exact about invariants, you can reap the algorithmic benefits.