[Python-Dev] PEP 487: Simpler customization of class creation (original) (raw)

INADA Naoki songofacandy at gmail.com
Tue Jun 21 19:09:09 EDT 2016

On Wed, Jun 22, 2016 at 2:50 AM, Raymond Hettinger <raymond.hettinger at gmail.com> wrote:

On Jun 21, 2016, at 10:18 AM, Guido van Rossum <guido at python.org> wrote:

Judging from Inada's message there seems to be some confusion about how well the compact dict preserves order (personally I think if it doesn't guarantee order after deletions it's pretty useless). Inada should follow PyPy's implementation of the compact dict which does preserve order after deletions (see below).

I follow it, for most cases.

When my compact dict doesn't preserve order is using PEP 412 Key sharing dict.

class A: ... ... ... a = A() b = A() # a and b shares same keys, and have each values a.a = 1 a.b = 2 # The order in shared key is (a, b) b.b = 3 b.a = 4 a.dict.items() dict_items([('a', 1), ('b', 2)]) b.dict.items() dict_items([('a', 4), ('b', 3)])

It's possible to split keys when the insertion order is not strictly same. But it decrease efficiency of key sharing dict.

If key sharing dict is effective only such a very strict cases, I feel slots can be used for it.

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