close_range.py

def close_range(start, step=1, count=None):
    i, orig_step = 0, step
    if count is None:
        count = start / step
    while i < count:
        yield start + (i * step)
        step *= -1
        if step != orig_step:
            i += 1
    return

print list(close_range(5))
[5, 4, 6, 3, 7, 2, 8, 1, 9]

iter_nearest.py

def iter_nearest(seq, idx, step=1, count=None):
    """
    >>> list(iter_nearest(range(10), 3))
    [3, 4, 2, 5, 1, 6, 0, 7, 8, 9]
    >>> list(iter_nearest(range(10), 3, count=5))
    [3, 4, 2, 5, 1]
    >>> list(iter_nearest(range(10), 3, step=-1))
    [3, 2, 4, 1, 5, 0, 6, 7, 8, 9]
    >>> list(iter_nearest(range(10), 3, step=-2))
    [3, 2, 5, 0, 7, 9]
    >>> list(iter_nearest(range(10), 3, count=0))
    []
    >>> list(iter_nearest(range(0), 3, count=5))
    []
    >>> list(iter_nearest(range(10), 100))
    [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
    """
    if count is None:
        count = len(seq)
    abs_step, len_seq = abs(step), len(seq)
    if step > 0:
        before = xrange(min(idx, len_seq - 1), -1, -abs_step)
        after = xrange(max(0, idx + 1), len_seq, abs_step)
        izipper = izip_longest(before, after)
    else:
        before = xrange(min(idx - 1, len_seq - 1), -1, -abs_step)
        after = xrange(max(0, idx), len_seq, abs_step)
        izipper = izip_longest(after, before)
    gen = (v for pair in izipper for v in pair if v is not None)
    i = 0
    while i < count:
        yield seq[next(gen)]
        i += 1
    return

iter_probe.py

def iter_probe(len_seq, idx, step=1, count=None):
    """Probe sequence indices up to but not including *len_seq* based on
    proximity to target index *idx*, according to *step* (1 goes up
    first, the default, whereas -1 down first), yielding a maximum of
    *count* indices. Yields only integers >= 0.

    >>> list(iter_nearest(range(10), 3))
    [3, 4, 2, 5, 1, 6, 0, 7, 8, 9]
    >>> list(iter_nearest(range(10), 3, count=5))
    [3, 4, 2, 5, 1]
    >>> list(iter_nearest(range(10), 3, step=-1))
    [3, 2, 4, 1, 5, 0, 6, 7, 8, 9]
    >>> list(iter_nearest(range(10), 3, step=-2))
    [3, 2, 5, 0, 7, 9]
    >>> list(iter_nearest(range(10), 3, count=0))
    []
    >>> list(iter_nearest(range(0), 3, count=5))
    []
    >>> list(iter_nearest(range(10), 100))
    [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
    """
    if count is None:
        count = len_seq
    abs_step = abs(step)
    if step > 0:
        before = xrange(min(idx, len_seq - 1), -1, -abs_step)
        after = xrange(max(0, idx + 1), len_seq, abs_step)
        izipper = izip_longest(before, after)
    else:
        before = xrange(min(idx - 1, len_seq - 1), -1, -abs_step)
        after = xrange(max(0, idx), len_seq, abs_step)
        izipper = izip_longest(after, before)
    gen = (v for pair in izipper for v in pair if v is not None)
    i = 0
    while i < count:
        yield next(gen)
        i += 1
    return