breamore...@gmail.com wrote: > On Monday, January 9, 2017 at 5:34:12 PM UTC, Tim Chase wrote: >> On 2017-01-09 08:31, breamoreboy wrote: >> > On Monday, January 9, 2017 at 2:22:19 PM UTC, Tim Chase wrote: >> > > I usually wrap the iterable in something like >> > > >> > > def pairwise(it): >> > > prev = next(it) >> > > for thing in it: >> > > yield prev, thing >> > > prev = thing >> > >> > Or from >> > https://docs.python.org/3/library/itertools.html#itertools-recipes:->> > >> > def pairwise(iterable): >> > "s -> (s0,s1), (s1,s2), (s2, s3), ..." >> > a, b = tee(iterable) >> > next(b, None) >> > return zip(a, b) >> > >> > This and many other recipes are available in the more-itertools >> > module which is on pypi. >> >> Ah, helpful to not have to do it from scratch each time. Also, I see >> several others that I've coded up from scratch (particularly the >> partition() and first_true() functions). >> >> I usually want to make sure it's tailored for my use cases. The above >> pairwise() is my most common use case, but I occasionally want N-wise >> pairing > > def ntuplewise(iterable, n=2): > args = tee(iterable, n) > loops = n - 1 > while loops: > for _ in range(loops): > next(args[loops], None) > loops -= 1 > return zip(*args) > >> >> s -> (s0,s1,…sN), (s1,s2,…S{N+1}), (s2,s3,…s{N+2}), … >> >> or to pad them out so either the leader/follower gets *all* of the >> values, with subsequent values being a padding value: >> >> # lst = [s0, s1, s2] >> (s0,s1), (s1, s2), (s2, PADDING) > > Use zip_longest instead of zip in the example code above. > >> # or >> (PADDING, s0), (s0, s1), (s1, s2) > > Haven't a clue off of the top of my head and I'm too darn tired to think > about it :)
In both cases modify the iterable before feeding it to ntuplewise(): >>> PADDING = None >>> N = 3 >>> items = range(5) >>> list(ntuplewise(chain(repeat(PADDING, N-1), items), N)) [(None, None, 0), (None, 0, 1), (0, 1, 2), (1, 2, 3), (2, 3, 4)] >>> list(ntuplewise(chain(items, repeat(PADDING, N-1)), N)) [(0, 1, 2), (1, 2, 3), (2, 3, 4), (3, 4, None), (4, None, None)] -- https://mail.python.org/mailman/listinfo/python-list
