[Python-Dev] Proposal: defaultdict

[Raymond Hettinger]

[Greg Ewing]
> Would people perhaps feel better if defaultdict
> *wasn't* a subclass of dict, but a distinct mapping
> type of its own? That would make it clearer that it's
> not meant to be a drop-in replacement for a dict
> in arbitrary contexts.

Absolutely.  That's the right way to avoid Liskov violations from altered 
invariants and API changes.  Besides, with Python's propensity for duck typing, 
there's no reason to subclass when we don't have to.


Raymond