alt Hacker News> Also worth noting that understanding changes over time. Remember when GvR and the rest of the core developers argued adamantly against ordered dictionaries? Haha! Good times!
The new implementation has saved space, but there are opportunities to save more space (specifically after deleting keys) that they've now denied themselves by offering the ordering guarantee.
Ordering, like stability in sorting, is an incredibly useful property. If it costs a little, then so be it.
This is optimizing for the common case, where memory is generally plentiful and dicts grow more than they shrink. Python has so many memory inefficiencies that occasional tombstones in the dict internal structure is unlikely to be a major effect. If you're really concerned, do `d = dict(d)` after aggressive deletion.