[Python-ideas] Allow isinstance second argument to be a set of types

[Greg Ewing]

Chris Rebert wrote:

> Why does it accept nested tuples in the first place for that matter?

Probably so that tuples could be used to emulate a "set
of types" before we had real sets.

Now that we do have real sets, it doesn't seem necessary
to continue with this and allow sets of sets, etc. So
+1 on leaving tuple as a special case for this and
treating all other iterables as flat.

-- 
Greg