To iterate over several generators in parallel, use the
for x, y in zip(a,b): print(x,y)
1 x 2 y 3 z
In python 2 you should use
itertools.izip instead. Here we can also see that the all the
zip functions yield tuples.
Note that zip will stop iterating as soon as one of the iterables runs out of items. If you'd like to iterate for as long as the longest iterable, use