Iterate adjacent pairs of elements in iter.
Options for mode:
abjad> list(listtools.pairwise(range(6)))
[(0, 1), (1, 2), (2, 3), (3, 4), (4, 5)]
abjad> list(listtools.pairwise(range(6), 'wrap'))
[(0, 1), (1, 2), (2, 3), (3, 4), (4, 5), (5, 0)]
abjad> list(listtools.pairwise(range(6), 9))
[(0, 1), (1, 2), (2, 3), (3, 4), (4, 5), (5, 0), (0, 1), (1, 2), (2, 3)]
This function returns a generator.