Is there a canonical way to check whether an iterable is ordered?

[Roy Smith]

In article <mailman.14103.1411047208.18130.python-list at python.org>,
 Chris Angelico <rosuav at gmail.com> wrote:

> The one thing you can rely on (and therefore must comply with, when
> you design an iterable) is that iteration will hit every element
> exactly once. 

Does it actually say that somewhere?  For example:

for i in bag.pick_randomly_with_replacement(n=5):
   print i

shouldn't do that.