[Python-Dev] dictnotes.txt out of date?

[Raymond Hettinger]

On Jun 13, 2012, at 10:35 AM, Eli Bendersky wrote:

> Did you mean to send this to the list, Raymond?


Yes.  I wanted to find-out whether someone approved changing
all the dict tunable parameters.   I thought those weren't supposed
to have changed.  PEP 412 notes that the existing parameters
were finely tuned and it did not make recommendations for changing them.

At one point, I spent a full month testing all of the tunable parameters
using dozens of popular Python applications.  The values used in Py3.2
represent the best settings for most apps.  They should not have been
changed without deep thought and substantial testing.

The reduction of the dict min size has an immediate impact on code
using multiple keyword arguments.

The reduced growth rate (from x4 to x2) negatively impacts apps that
have a dicts with a steady size but constantly changing keys
(removing an old key and adding a new one).  The lru_cache is
an example.   The reduced growth causes it to resize much more
frequently than before.

I think the tunable parameters should be switched back to what they
were before.  Tim and others spent a lot of time getting those right
and my month of detailed testing confirmed that those were excellent
choices.

The introduction of Mark's shared-key dicts was orthogonal to the
issue of correct parameter settings.  Those parameters did not have
to change and probably should not have been changed.


Raymond

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