Antoon Pardon wrote:
Op 2004-12-21, Jeff Shannon schreef <[EMAIL PROTECTED]>:
How does the dict know which value is associated with which key?
Because there is a link between the key and the value. The problem
with a mutated key in a dictionary is not that the link between the
key and the value is severed, but that the key hashes now to a different
bucket. But if you just go over the buckets and iterate over the keys
within and there associated values, you will encouter your mutated
key with its value.
Except that the hash value *IS* the link between the key and the value. You cannot change the hash value without severing the link. You cannot trace the link without the original hash value. You do not have the original hash value when accessing the dict with a mutated key.
I need to be able to access sequence-keyed dictionaries with literals, which means that the keys need to compare by value, not ID. Thus, I need to have sequences that compare (and hash) by value. These conditions *cannot* be met by a mutable list.
Which condition can't be met by a mutable list? The only ones I see
above is comparison and hashable by value. A list can be compared
and hashed by value.
A list cannot be hashed by value in such a way that the hash doesn't change when the list mutates.
I can have the quality of hash value not changing when mutated, or I can have the quality of hashing by value, but I *cannot* have both.
So? You don't need the first.
That's an "interesting" assertion. You have yet to provide any evidence of it, however.
Thus, even if you make lists hash by ID, I *still* need to have an immutable tuple type so that I can get hash-by-value.
No you don't. The same algorithm that works for hashing tuples will
work just as fine for hashing lists.
Except that the hash value will change when the list mutates, and then I can't access my dictionary values.
Jeff Shannon Technician/Programmer Credit International
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