In fact official python docs say: "The left-to-right evaluation order of the iterables is guaranteed. This makes possible an idiom for clustering a data series

In fact official python docs say: "The left-to-right evaluation order of the iterables is guaranteed. This makes possible an idiom for clustering a data series into n-length groups using zip([iter(s)]n)." http://docs.python.org/2/library/functions.html#zip http://docs.python.org/2/library/functions.html#zip