On 07/15/2015 10:53 PM, Ben Finney wrote:
Steven D'Aprano <st...@pearwood.info> writes:
You can't use a dict for the mapping, not unless you're smarter than
me, due to the requirement to hash the keys.
Dang. It's the mapping that I really need to solve, I think. A mapping
that has a custom “does this candidate match any existing key” and
“return the value for this key” to defer to the matching behaviour
described above.
Are those the ‘__contains__’, ‘__getitem__’ methods? What actually is
the API of a mapping type, that would need to be customised for this
application?
The problem is that potential key matches are found by hashes, and the hash of
('value1', ANY, 'next_value')
and
('value1, 'value2', 'next_value')
and
('value1', 'value3', 'next_value')
will not and cannot be the same.
If you fiddle with your object such that all instances hash to the same value
then you lose the O(1) lookup for the dict -- you basically have a list.
--
~Ethan~
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