[Python-Dev] Question about dictobject.c:lookdict_string

[Eyal Lotem]

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.