There's a simple function that I use many times, and I think may be a good fit to be added to itertools. A function that gets an iterator, and if it has exactly one element returns it, and otherwise raises an exception. This is very useful for cases where I do some sort of query that I expect to get exactly one result, and I want an exception to be raised if I'm wrong. For example:
jack = one(p for p in people if p.id
This is my implementation:
it = iter(iterable)
r = next(it)
raise ValueError("Iterator is empty")
raise ValueError("Iterator has more than one item")
What do you think?