[Python-Dev] Python 3.6 dict becomes compact and gets a private version; and keywords become ordered (original) (raw)

Dima Tisnek dimaqq at gmail.com
Wed Sep 21 06:10:33 EDT 2016

I guess what lru_cache needs is atomic push-pop:

on hit: pop(this) + push_back(this) on miss: pop_front() + push_back(this)

I reckon, if flat array is lazy (i.e. can grow larger than no. of keys), then amortised push-pop performance is not hard to achieve.

Overall, it sounds more like heap queue;

And it's a great example of feature creep -- once ordered dicts are builtin, every one and their niece wants to use them, not necessarily what they were originally envisioned for.

By comparison, **kwargs and **meta are statistically mostly immutable.

Perhaps distinct specialisations are better?

On 20 September 2016 at 13:11, INADA Naoki <songofacandy at gmail.com> wrote:

On Tue, Sep 20, 2016 at 7:02 PM, INADA Naoki <songofacandy at gmail.com> wrote:

On Tue, Sep 20, 2016 at 6:56 PM, Dima Tisnek <dimaqq at gmail.com> wrote:

Totally random thought:

Can lrucache be simplified to use an ordered dict instead of dict + linked list?

I think so. See also: http://bugs.python.org/issue28199#msg276938 FYI, current dict implementation is not optimized for removing first item like this: _ _// When hit maxsize_ _Pyssizet pos;_ _PyObject *key;_ _if (PyDictNext(d, &pos, &key, NULL)) {_ _if (PyDictDelItem(key) < 0) {_ _// error._ _}_ _}_ _ So, before changing lrucache implementation, I (or someone else) should rewrite OrderedDict which has O(1) "remove first item" method. (At least maxsize is not None). But both of OrderedDict and lrucache improvements can't be in 3.6 since 3.6 is beta now. I'll try it after 3.6rc1. -- INADA Naoki <songofacandy at gmail.com>

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