@ChrisA: Shadowing "iter()" would only help with Barry's example. @Jonathan: Updating documentation is helpful, but I find an automated check better. Too often the most obvious way to accomplish something silently triggers this behavior: strings = ['aa', '', 'bbb', 'c'] strings = filter(bool, strings) # Adding this step makes n_unique always 0. longest = max(strings, key=len) n_unique = len(set(strings)) I feel like a warning here would save time and prevent bugs, and that my is_exhausted proposal, if implemented directly in the generators, is an easy way to accomplish this. And I have to say I'm surprised by the responses. Does nobody else hit bugs like this and wish they were automatically detected? To be clear, raising ValueError is just an example; logging a warning would already be helpful, like Go's race condition detector. -- BoppreH