acc.py

r"""
Ref: https://www.pttweb.cc/bbs/Python/M.1398877470.A.1E7

>>> data = list(range(22)); seglen = 4
>>> list(map(lambda E,T=[0]:T.__setitem__(0,E[1]+(E[0]%seglen and T[0])) or T[0], enumerate(data)))
[0, 1, 3, 6, 4, 9, 15, 22, 8, 17, 27, 38, 12, 25, 39, 54, 16, 33, 51, 70, 20, 41]
>>> x = []
>>> for i, v in enumerate(data):
...     x.append(v+x[i-1] if i%seglen!=0 else v)
...
>>> x
[0, 1, 3, 6, 4, 9, 15, 22, 8, 17, 27, 38, 12, 25, 39, 54, 16, 33, 51, 70, 20, 41]
>>> def f(xs, count=0, ys=()):
...     if not xs:
...         return ys
...     else:
...         return f(xs[1:], (count+1)%seglen, ys+(xs[0]+(0 if count==0 else ys[-1]),))
...
>>> f(data)
(0, 1, 3, 6, 4, 9, 15, 22, 8, 17, 27, 38, 12, 25, 39, 54, 16, 33, 51, 70, 20, 41)
>>> from itertools import chain
>>> def g(xs, count=0, ys=(), last=0):
...     try:
...         x = next(xs)
...         y = x + (0 if count==0 else last)
...         yield from g(xs, (count+1)%seglen, chain(ys, (y,)), y)
...     except StopIteration:
...         yield from ys
...
>>> tuple(g(iter(data)))
(0, 1, 3, 6, 4, 9, 15, 22, 8, 17, 27, 38, 12, 25, 39, 54, 16, 33, 51, 70, 20, 41)
"""