... because the former does not imply the latter anyways, e.g.
generators are iterables but unsized.
Now `plot(zip([1, 2], [3, 4]))` (py3) raises `RuntimeError: matplotlib
does not support generators` (from `cbook.safe_first_element`) which is
probably the intended exception, rather than `TypeError: object of type
'zip' has no len()`. Perhaps this exception should be changed to a
`TypeError`, by the way...