[Python-Dev] Question about dictobject.c:lookdict_string (original) (raw)

Eyal Lotem eyal.lotem at gmail.com
Mon Jun 11 06:55:50 CEST 2007

My question is specifically regarding the transition back from lookdict_string (the initial value) to the general lookdict.

Currently, when a string-only dict is trying to look up any non-string, it reverts back to a general lookdict.

Wouldn't it be better (especially in the more important case of a string-key-only dict), to revert to the generic lookdict when a non-string is inserted to the dict, rather than when one is being searched?

This seems to me as it would shift this (admittedly very slight) performance cost of a type ptr comparison from the read-access, to write-access on all dicts (which means insertions of new keys in non-string-only dicts may pay for another check, or that the lookdict funcptr will be replaced by two funcptrs so that a different insertion func on string-only dicts is used too [was tempted to say vtable here, but that would add another dereference to lookups]).

It would also have the slight benefit of speeding up non-string lookups in string-only dicts.

This does not seem like a significant issue, but as I know a lot of effort went into optimizing dicts, I was wondering if I am missing something here.

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