Brian Harring schrieb: >> I think this is incorrect. The implementation could well support it, >> putting a dummy object into the deleted key (which deletion needs >> to do, anyway). > > The implementation already uses a sentinel (NULL)-
That' not the full truth. The implementation has a separate object (called the dummy object, see dictobject.c:140 in the trunk) to fill put in for deleted objects. You can't use NULL here because then the open addressing would break. NULL is used as a sentinel for the open addressing; the dummy object indicates that you have to continue searching. > point was that it > does not support iteration over a dict that's being deleted from > *currently* though. Yes, but I believe that's out of fear that you have to do resizing; iteration cannot be supported in the presence of resizing. Deletion does not involve resizing, instead, ma_fill won't decrease during deletion, so the next addition may trigger resizing if the fill level goes above 2/3. > One thing to note; delitem is the easy case. Allowing for mutating > the mapping as you're iterating via delitem implies that setitem > should work also; setitem however can trigger a resize. So that implication is wrong, no? Of course, setitem for an existing key could be allowed; that's also a meaningful operation while you are iterating over a dictionary. > Finally, if dicts were ever modified to shrink based on load, the > resize there would be an issue. Mind you I've not seen proposals of > that sort, just pointing out the potential. You'd have to defer the resizing while the dictionary is locked. > In my opinion, no point in doing the deltitem modification without a > matching setitem. Not saying I think the modification is worth it > mind you, just that there should be symmetry ;) IMO, it is clear that this symmetry is *not* necessary, for the reason that we are discussing: if iterators where to support a delete operation, then it would be possible to provide that for dict iterators. It wouldn't be necessary to support any other updates; it wouldn't even be necessary to support del d[k], even if k is the key returned from the iterator's .next(). Regards, Martin _______________________________________________ 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
