Merge multiple sorted inputs into a single sorted output. Similar to sorted(itertools.chain(*iterables)) but returns a generator, does not pull the data into memory all at once, and assumes that each of the input streams is already sorted (smallest to largest). >>> list(merge([1,3,5,7], [0,2,4,8], [5,10,15,20], [], [25])) [0, 1, 2, 3, 4, 5, 5, 7, 8, 10, 15, 20, 25] If *key* is not None, applies a key function to each element to determine its sort order. >>> list(merge(['dog', 'horse'], ['cat', 'fish', 'kangaroo'], key=len)) ['dog', 'cat', 'fish', 'horse', 'kangaroo']