Why is Python's OrderedDict ordered?
10 comments
·October 30, 2025addaon
recursivecaveat
I was under that impression as well, but it was added as an implementation in 3.6 (https://bugs.python.org/issue27350), so I don't know that too many people would have become dependent on it before it was official in 3.7: https://docs.python.org/3/whatsnew/3.7.html
I think the "how/why" thing is just the automatic title de-clickbait-ifer going a little haywire?
DemocracyFTW2
I don't think this is the "why". What you're depicting is what happened in JavaScript. Dictionary keys in Python always had that (to me) annoying property that they preserved insertion order until they don't. I'd frankly much prefer if they'd always be iterated in random order each time they're traversed.
not_kurt_godel
I'd love to see the results of mandating a random order dict impl at an actual company/org (but hate to be forced to participate). Hopefully you hired developers who really like to write sorting algos.
nielsbot
Swift (heavily used by Apple) has randomly ordered dictionaries for security:
> In particular, random seeding enables better protection against (accidental or deliberate) hash-flooding attacks
https://forums.swift.org/t/psa-the-stdlib-now-uses-randomly-...
yxhuvud
Well, that is how hash tables in go works, so you'd not have to look that far.
DemocracyFTW2
Wrong title, article has "How Does Python’s OrderedDict Maintain Order?"
Title of the article is "How…", not "Why…", and "why" is not discussed. (My understanding is that the "why" is "because the implementation acted that way without an official guarantee, and folks depended on the implementation detail, so it became guaranteed.)