Yes, we should not. But we can do this when use map function. the document gives a good example but doesn't say much about real differences between map and imap. Maybe we should add some notes like INADA suggest. 

map function will convert iterable to list if it doesn't implement __len__ function, so if you are using a generator, you should consider use imap. As well as add a warning about don't try to access the result outside the with statement. 

But if you guys think the docs are good enough, please close this issue.