A “frozen” dictionary for Python

I wonder whether Raymond Hettinger has an opinion on this PEP. A long time ago, he wrote: "freezing dicts is a can of worms and not especially useful".

https://mail.python.org/pipermail/python-dev/2006-February/0...

That's a great link and recommended reading.

It explains a lot about the design of Python container classes, and the boundaries of polymorphism / duck typing with them, and mutation between them.

I don't always agree with the choices made in Python's container APIs...but I always want to understand them as well as possible.

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! Thank goodness their first wave of understanding wasn't their last. Concurrency and parallelism in Python was a TINY issue in 2006, but at the forefront of Python evolution these days. And immutability has come a long way as a design theme, even for languages that fully embrace stateful change.

> 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.

> Ordering, like stability in sorting, is an incredibly useful property.

I can't say I've noticed any good reasons to rely on it. Didn't reach for `OrderedDict` often back in the day either. I've had more use for actual sorting than for preserving the insertion order.

Same. Recently I saw interview feedback where someone complained that the candidate used OrderedDict instead of the built-in dict that is now ordered, but they'll let it slide... As if writing code that will silently do different things depending on minor Python version is a good idea.

Honestly, if I was writing some code that depended on dicts being ordered I think I'd still use OrderedDict in modern Python. I gives the reader more information that I'm doing something slightly unusual.