[Python-Dev] A new dictionary implementation (original) (raw)

Steven D'Aprano steve at pearwood.info
Mon Jan 30 00:30:14 CET 2012

Mark Shannon wrote:

Antoine Pitrou wrote:

On Sun, 29 Jan 2012 09:56:11 -0500 Benjamin Peterson <benjamin at python.org> wrote:

2012/1/29 Mark Shannon <mark at hotpy.org>: Hi,

Now that issue 13703 has been largely settled, I want to propose my new dictionary implementation again. It is a little more polished than before. If you're serious about changing the dictionary implementation, I think you should write a PEP. It should explain the new dicts advantages (and disadvantages?) and give comprehensive benchmark numbers. Something along the lines of http://www.python.org/dev/peps/pep-3128/ I should think. "New dictionary implementation" is a misnomer here. Mark's patch merely allows to share the keys array between several dictionaries. The lookup algorithm remains exactly the same as far as I've read. It's actually much less invasive than e.g. Martin's AVL trees-for-hash-collisions proposal. Antoine is right. It is a reorganisation of the dict, plus a couple of changes to typeobject.c and object.c to ensure that instance dictionaries do indeed share keys arrays.

I don't quite follow how that could work.

If I have this:

class C: pass

a = C() b = C()

a.spam = 1 b.ham = 2

how can a.dict and b.dict share key arrays? I've tried reading the source, but I'm afraid I don't understand it well enough to make sense of it.

-- Steven

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