[Python-Dev] calling dictresize outside dictobject.c (original) (raw)

Dan Schult dschult at colgate.edu
Tue Apr 7 05:47:17 CEST 2009

Hi, I'm trying to write a C extension which is a subclass of dict. I want to do something like a setdefault() but with a single lookup.

Looking through the dictobject code, the three workhorse routines lookdict, insertdict and dictresize are not available directly for functions outside dictobject.c, but I can get at lookdict through dict->ma_lookup().

So I use lookdict to get the PyDictEntry (call it ep) I'm looking for. The comments for lookdict say ep is ready to be set... so I do that. Then I check whether the dict needs to be resized--following the nice example of PyDict_SetItem. But I can't call dictresize to finish off the process.

Should I be using PyDict_SetItem directly? No... it does its own
lookup. I don't want a second lookup! I already know which entry will be
filled.

So then I look at the code for setdefault and it also does a double lookup for checking and setting an entry.

What subtle issue am I missing? Why does setdefault do a double lookup? More globally, why isn't dictresize available through the C-API?

If there isn't a reason to do a double lookup I have a patch for
setdefault, but I thought I should ask here first.

Thanks! Dan

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