codekingpro/portable-devtools

1# from more_itertools 9.02def only(iterable, default=None, too_long=None):3    """If *iterable* has only one item, return it.4    If it has zero items, return *default*.5    If it has more than one item, raise the exception given by *too_long*,6    which is ``ValueError`` by default.7    >>> only([], default='missing')8    'missing'9    >>> only([1])10    111    >>> only([1, 2])  # doctest: +IGNORE_EXCEPTION_DETAIL12    Traceback (most recent call last):13    ...14    ValueError: Expected exactly one item in iterable, but got 1, 2,15     and perhaps more.'16    >>> only([1, 2], too_long=TypeError)  # doctest: +IGNORE_EXCEPTION_DETAIL17    Traceback (most recent call last):18    ...19    TypeError20    Note that :func:`only` attempts to advance *iterable* twice to ensure there21    is only one item.  See :func:`spy` or :func:`peekable` to check22    iterable contents less destructively.23    """24    it = iter(iterable)25    first_value = next(it, default)26 27    try:28        second_value = next(it)29    except StopIteration:30        pass31    else:32        msg = (33            'Expected exactly one item in iterable, but got {!r}, {!r}, '34            'and perhaps more.'.format(first_value, second_value)35        )36        raise too_long or ValueError(msg)37 38    return first_value39