←back to thread

A “frozen” dictionary for Python

(lwn.net)
191 points jwilk | 1 comments | 11 Dec 25 09:51 UTC | HN request time: 0s | source
Show context
perrygeo ◴[11 Dec 25 15:02 UTC] No.46232229[source]▶
Python discovers immutable data, and gets it wrong. Frozendict is a blunt instrument - instead of a mutable free-for-all, it just locks the data for the entire lifecycle. Brace for the wave of code littered with deep copies, proudly proclaiming how functional it all is.

If you want real immutable data structures, not a cheap imitation, check out pyrsistent.

replies(2): >>46232356 #>>46232421 #
shadowgovt ◴[11 Dec 25 15:12 UTC] No.46232356[source]▶
If your dicts are frozen, you shouldn't need to deep-copy. The point of immutability is that if you want a new frozendict based on another one, you just rebuild the indirection data structure up top and leave the values it references alone.
replies(1): >>46233892 #
perrygeo ◴[11 Dec 25 16:58 UTC] No.46233892[source]▶
You're absolutely right: an "indirection data structure" is necessary. Freezing the data is the least interesting part - it doesn't give you any of the benefits typically associated with immutable data structures in functional languages. That's my point - Python is shipping a half solution that's being mistaken for a proper one.

You think Python developers are going to roll their own HAMT on top of frozendicts? Or are they just gonna make copies? Personally, I'd just use pyrsistent which seems to get it right.

replies(3): >>46234888 #>>46234947 #>>46254141 #
1. rented_mule ◴[11 Dec 25 18:19 UTC] No.46234947[source]▶
It's a little early to say that "Python is shipping" anything related to this. The PEP is still in draft status and it may be modified (as it was three hours ago) or even rejected. The article says it is likely to be accepted, but that has not happened yet. That also means there is time to comment on the PEP in the discussion it links to if you'd like.

https://peps.python.org/pep-0814/