Why is dictionary.keys() a list and not a set?

["Martin v. Löwis"]

Mike Meyer wrote:
>>I trusted the doco which defines a set as "an unordered collection of
>>immutable values" (http://docs.python.org/lib/types-set.html).
> 
> 
> If the hash changes, you've screwed up the set. What it really should
> say is "collection of objects with fixed hashes", or words to that
> effect. Do you want to file a PR on this?

It's more than that: you really mean "hashable values", where "hashable"
does not just imply that the hash value is fixed, but also that the
equal objects hash same.

Regards,
Martin