Hash of None varies per-machine

Paul Rubin http
Fri Apr 3 19:57:05 CEST 2009


ben.taylor at email.com writes:
> 1. Is it correct that if you hash two things that are not equal they
> might give you the same hash value?

Yes, hashes are 32 bit numbers and there are far more than 2**32
possible Python values (think of long ints), so obviously there must
be multiple values that hash to the same slot.

> 2. Should the hash of None vary per-machine? 

If the docs say this shouldn't happen, then it's a bug.  Otherwise,
it should probably be considered ok.

> 3. Given that presumably not all things can be hashed (since the
> documentation description of hash() says it gives you the hash of the
> object "if it can be hashed"), should None be hashable?

Yes, anything that can be used as a dict key (basically all immutable
values with equality comparison) should be hashable.



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