Op 2004-12-21, Nick Coghlan schreef <[EMAIL PROTECTED]>: > Antoon Pardon wrote: >> Why then doesn't python think the same about sorted lists. When I have a >> sorted list and do operations on it that depend on it being sorted, >> I can mess things up just as easily by mutating an element in that >> sorted list as I can mess things up by mutating a dictionary key. > > Incorrect, and this appears to be the point where our major disagreement lies. > > Mutate a value in a sorted list and you can fix that easily, just by calling > its > sort() method again (and, in fact, mutate and resort is a fairly common idiom > for small datasets). 'sorted' and 'heapified' are list properties that are > easily broken by direct manipulation, but are also easily restored by once > again > 'sorting' or 'heapifying'.
That is an implemantation detail. Likewise a dictionary is probably not always in a sane state when a new key is inserted. The fact remains that in a sorted list or a heap, mutating an element arbitrarily can mess up things greatly. > Change the hash value of an item used as a key in a dictionary, and *the > internal state of the dictionary is likely to broken in a manner you probably > cannot fix*. The only reason the 'probably' is there is because you should be > able to 'fix it' by changing the hash value back to what it was originally. I could argue that this is then a failing of dictionary that doesn't provide a method to clean up after a key is mutated. > Waitasec - wouldn't it be easier if dictionaries just made it a rule that the > hash value wasn't allowed to change? Hang on, that's exactly what they do. No it is not. And yes I know what to do if I want to use mutable keys as objects. I'm just argueing against those who think that should be somehow forbidden. -- Antoon Pardon -- http://mail.python.org/mailman/listinfo/python-list
