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

[Peter Hansen]

bonono at gmail.com wrote:
> Which is also my initial puzzle, items() and iteritems() already gives
> you the tuples, why such gurantee or the others ? Doesn't that violate
> the general idiom that if we can do certain thing in one way, there
> better be one and only one way.
> 
> Are there other usage scenarios that would be benefit from this as the
> example given is not convincing for me.

As Jeff's reply emphasizes, the "examples" show tuples with *value* and 
then *key*, not the other way around which is what .items() and 
.itemitems() gives you.

Anyway, you didn't ask for good examples of use, just "why is it 
guaranteed", and that's all I was showing you.  Whether it was a good 
idea might be an interesting discussion, but probably not a particularly 
useful one given once again that it's unlikely this particular feature 
could be undone now that code exists (we can assume) which is dependent 
on it.

-Peter