Movatterモバイル変換
[0]ホーム
[Python-Dev] Re: Sets: elt in dict, lst.include
M.-A. Lemburgmal@lemburg.com
Mon, 29 Jan 2001 19:08:16 +0100
Guido van Rossum wrote:>> > Dictionaries are not sequences. I wonder what order a user of> > for k,v in dict: (or whatever other of this proposal you choose)> > will expect...>> The same order that for k,v in dict.items() will yield, of course.And then people find out that the order has some sortingproperties and start to use it... "how to sort a dictionary?"comes up again, every now and then. > > Please also take into account that dictionaries are *mutable*> > and their internal state is not defined to e.g. not change due to> > lookups (take the string optimization for example...), so exposing> > PyDict_Next() in any to Python will cause trouble. In the end,> > you will need to create a list or tuple to iterate over one way> > or another, so why bother overloading for-loops w/r to dictionaries ?>> Actually, I was going to propose to play dangerously here: the>> for k:v in dict: ...>> syntax I proposed in my previous message should indeed expose> PyDict_Next(). It should be a big speed-up, and I'm expecting (though> don't have much proof) that most loops over dicts don't mutate the> dict.>> Maybe we could add a flag to the dict that issues an error when a new> key is inserted during such a for loop? (I don't think the key order> can be affected when a key is *deleted*.)You mean: mark it read-only ? That would be a "nice to have"property for a lot of mutable types indeed -- sort of likelow-level locks. This would be another candidate for an object flag(much like the one Fred wants to introduce for weak referencedobjects).-- Marc-Andre Lemburg______________________________________________________________________Company:http://www.egenix.com/Consulting:http://www.lemburg.com/Python Pages:http://www.lemburg.com/python/
[8]ページ先頭