[Python-Dev] gc ideas -- sparse memory (original) (raw)

Stephen J. Turnbull stephen at xemacs.org
Sat Dec 4 13:33:06 CET 2010

Steven D'Aprano writes:

Martin v. Löwis wrote:

It seems counter-productive to me to bother with an identity function which doesn't meet that constraint. If id(x) == id(y) implies nothing about x and y (they may, or may not, be the same object) then what's the point?

See James' explanation: it would be possible to use this as the foundation of an identity hash table.

I'm afraid James' explanation didn't shed any light on the question to me. It seems to me that Java's IdentityHashValue[sic -- I think the correct function name is actually IdentityHashCode] is equivalent to Python's hash(), not to Python's id(), and claiming it is related to identity is misleading and confusing.

Not quite equivalent. Python's hash() obeys a certain additional constraint (that numeric values that compare equal have the same hash), and IdentityHashValue presumably won't work at all on numbers in Java (since they aren't objects).

Bikeshedding aside, I have to agree with you: there's no point in calling such a function id() or IdentityAnything(). Everything you need to know (including both the fact that it could be an efficient way to search for a unique object, and the possible non-uniqueness of the object assigned that code) is contained in the word "hash".

More information about the Python-Dev mailing list