A custom iterators for me :D

myitertools.py

import itertools
import math

def defer(l, num_defer=1):
    """
    >>> [x for x in defer([0, 1, 2, 3])]
    [[0, 1], [1, 2], [2, 3]]

    >>> [x for x in defer([0, 1, 2, 3], 2)]
    [[0, 2], [1, 3]]
    """
    its = itertools.tee(l, 2)
    for current, next in itertools.izip(its[0], itertools.islice(its[1], num_defer, None)):
        yield [current, next]


def diffs(iter_of_iter):
    """
    >>> for x in diffs([[0, 1, 2], [1, 2, 3], [3, 4, 5]]):
    ...     print x
    [1, 1, 1]
    [2, 2, 2]
    """

    for current, next in defer(iter_of_iter):
        yield itertools.imap(lambda x: x[1] - x[0], itertools.izip(current, next))


def pow2sum(l):
    """
    >>> pow2sum([1, 2, 3])
    14
    """
    
    return sum((x ** 2 for x in l))

def speeds2(iter_of_iter):
    """
    >>> for x in speeds2([[0, 0, 0], [1, 0, 0], [2, 2, 2]]):
    ...     print x
    1
    9
    """
    return (pow2sum(x) for x in diffs(iter_of_iter))


def speeds(iter_of_iter):
    """
    >>> for x in speeds([[0, 0, 0], [1, 0, 0], [2, 2, 2]]):
    ...     print x
    1.0
    3.0
    """
    return (pow2sum(x) ** 0.5 for x in diffs(iter_of_iter))

def _test():
    import doctest
    doctest.testmod()


if __name__ == "__main__":
    _test()