groups_of.py

def groups_of(n, xs, **kwargs):
    """
    Returns n elements from xs until empty.
    Optional 'pad' keyword argument will pad a value to the resulting iterator
    to meet
    >>> for x in groups_of(2, [1, 2, 3, 4, 5]):
    ...     print x
    [1, 2]
    [3, 4]
    [5]
    >>> for x in groups_of(3, [1, 2, 3, 4, 5], pad=None):
    ...     print x
    [1, 2, 3]
    [4, 5, None]
    """
    if 'pad' in kwargs:
        pad, use_padding = kwargs.pop('pad'), True
    else:
        pad, use_padding = None, False
    xs = iter(xs)
    while True:
        result = []
        for i in range(n):
            try:
                result.append(xs.next())
            except StopIteration:
                if result:
                    if use_padding:
                        result += [pad] * (n - i)
                    yield result
                return
        yield result