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

[Peter Hansen]

bonono at gmail.com wrote:
> Please don't take it as a challenge, it was not. If it was, it was
> about the need for the guarantee, not about you not giving me the
> answer I want. But it is really wondering why ?

If you really want to know merely the *need* for the guarantee, as in 
why was this ever put in in the first place, you will be sure of a 
correct answer only if it's provided by those who wrote the code in the 
first place.  Anything else is guessing or mind-reading.  I wasn't 
trying to do even that, but just to point to where I had seen the 
afore-mentioned guarantee.  My responsibility ended there, and with that 
I am outta here. :-)

-Peter

(And don't worry, I didn't take it as a challenge.  If you thought I 
took offense somewhere, please re-read my words without that thought in 
mind and I think you'll see merely straight-forward factual responses to 
your questions, as they were meant to be.  Cheers.)