Hi Dan, Thanks for your interest. 2009/4/6 Dan Schult <dsch...@colgate.edu>: > 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?
Because it's not useful outside the intimate implementation details of dictobject.c > > 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. Raymond tells me the cost of the second lookup is negligible because of caching, but PyObject_Hash needn't be called two times. He's working on a patch later today. -- Regards, Benjamin _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
