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Comment by samdk | Hacker News Reader

Python and Ruby both have separate arrays and hashes. They're completely different data structures in both cases.

Python's dict type is a hash table like you'd expect. Python's list is a pointer-array-backed list. (it may inline ints/similar things--I don't remember if CPython does, and exact details are implementation-dependent), and raw arrays are in the standard library if you need them.

From a very quick check, a list of 100k ints in CPython is ~1.5mb, and a dict of 100k ints -> other ints is ~6mb.

Ruby's hash and array implementations are similar, I think, although I don't know Ruby as well, so I don't know the specifics.

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Good info about Python, but you are incorrect about Ruby. Hashes and arrays are totally different in the Ruby implementations I know of.

EDIT: Sorry, I misread you. Ruby MRI and CPython are indeed similar.

At least in Ruby MRI (the mainline) arrays are implemented as a struct with a size and a pointer to a normal C array which contains the object references (references in MRI are pointers to object structs which use the lower bits to inline integers of <= 31 or 63 bits, true, false, nil and symbols).

Hashes in MRI I have not looked that much into but I believe they are a hash tables which in ruby 1.9 retain insertion order using pointers like a singly linked list.

> Good info about Python, but you are incorrect about Ruby. Hashes and arrays are totally different in the Ruby implementations I know of.

From its context, I'm guessing samdk is saying:

> Ruby's hash and array implementations are similar [to Python's dict and list]

not that they're similar to one another, which would make absolutely no sense considering his comment starts with:

> Python and Ruby both have separate arrays and hashes.

so I'd say you agree with him and misread his comment.

Does python have standard implementation of odict already?

It's nice that Python and Ruby have data structures that trade some features for some memory and/or performance gain.

> Does python have standard implementation of odict already?

Yeppers, since 2.7/3.1: http://docs.python.org/library/collections.html#collections.... http://docs.python.org/py3k/library/collections.html#collect...

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