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

Victor Stinner victor.stinner at gmail.com
Mon Sep 12 08:36:53 EDT 2016

2016-09-12 13:50 GMT+02:00 Antoine Pitrou <solipsis at pitrou.net>:

Besides, I don't think it has been proven that the compact-and-ordered dict implementation is actually faster than the legacy one.

Python 3.6 dict is slower than Python 3.5 dict, at least for a simple lookup: http://bugs.python.org/issue27350#msg275581

But its memory usage is 25% smaller.

I'm curious about the performance of the "compaction" needed after adding too many dummy entries (and to preserve insertion order), but I don't know how to benchmark this :-) Maybe add/remove many new keys? I expect bad performance on the compaction, but maybe not as bad as the "hash DoS".

For regular Python code, I don't expect compaction to be a common operation, since it's rare to remove attributes. It's more common to modify attributes value, than to remove them and later add new attributes.

Victor

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