Ulrich Eckhardt wrote:
Ethan Furman wrote:
Several folk have said that objects that compare equal must hash equal,
and the docs also state this
http://docs.python.org/dev/reference/datamodel.html#object.__hash__
I'm hoping somebody can tell me what horrible thing will happen if this
isn't the case?
If you were familiar with what a hash map is, you wouldn't ask. The thing is
that the hash is used to look up the place in the map where the thing is
stored. If two equal objects have different hashes, they will be stored in
different places in the hash map. Looking for object1 will then not turn up
with object2, even though they are equal.
In this case this is the behavior I want.
If this is something you don't
care about, and all you care about is identity, then I'd derive the hash
from each object's ID.
This won't work, as objects of the same type that compare equal should
(and do, in my code) hash equal.
This ID has another property which is something that is assumed for hashes,
and your code seems a bit to get that wrong, too, and that is that the hash
must not change.
The hash does not change on the instances, and is the same for all
instances of my type that compare equal.
~Ethan~
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