Op 2004-12-15, Fredrik Lundh schreef <[EMAIL PROTECTED]>: > Antoon Pardon wrote: > >>> how would you implement a dictionary where the keys could change, without >>> any performance penalty compared to the current implementation? >> >> The performace gained by using tuples as keys in dictionaries is >> entirely illusional. >> >> Sure the fact that you use a tuple which is immutable, makes that >> you can put the key directly in the dictionary instead of a copy >> and that will gain you some performance. >> >> But this performance gain can be more than offset by other code >> in the program. >> >> Suppose you need a list/tuple as a key and most opperation you >> will do on those keys will be appends and pops. You now have the >> itwo choices >> >> 1) Always convert your lists to tuples on key entries >> and keys accesses, which will mean more copying than when a >> copy of a key would have been made on key entry. >> >> 2) Simulate appends and pops by tuple operations which can also >> require more copying than was gained by using tuples as key > > sorry, but I don't understand your reply at all. are you saying that > dictionaries > could support mutable keys (e.g lists) by making a copy of the key? how would > such a dictionary pick up changes to the original key object? (I'm talking > about > the key stored in the dictionary, not the key you're using to look things up).
You want to mutate a key that is within a dictionary? That sounds as bad as mutating an element in a sorted list. -- Antoon Pardon -- http://mail.python.org/mailman/listinfo/python-list
