[docs] [issue23677] Mention dict and set comps in library reference

[Martin Panter]

Martin Panter added the comment:

The distiction about non-empty sets is a bit misleading. You can create an empty set via comprehension:

>>> {x for x in ()}
set()

----------
nosy: +martin.panter

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue23677>
_______________________________________