def one(iterable):
    """Return the single element in iterable.

	Raise an error if there isn't exactly one element.
	"""
    item = None
    iterator = iter(iterable)
    try:
        item = next(iterator)
    except StopIteration:
        raise ValueError('Iterable is empty, must contain one item')
    try:
        next(iterator)
    except StopIteration:
        return item
    else:
        raise ValueError('object contains >1 items, must contain exactly one.')
