Example

Question

why is that works so:
nums = list(accumulate(range(8))) ?

Answer 1

It helps to do things in the python shell, one at a time. Extra steps are here for hints:

>>> from itertools import accumulate
>>> list(accumulate(range(8)))
[0, 1, 3, 6, 10, 15, 21, 28]

>>> print(range(8))
range(0, 8)

>>> list(range(8))
[0, 1, 2, 3, 4, 5, 6, 7]

>>> accumulate(range(8))
<itertools.accumulate object at 0xb6af7ff0>

>>> list(accumulate(range(8)))
[0, 1, 3, 6, 10, 15, 21, 28]

loop accumulator
0 0
1 1 (0+1)
2 1+2=3 (new value)
3 3+3=6
4 6+4=10
5 10+5=15
etc.

Another example, accumulating 1 four times, then 2 on the last iteration:

>>> list(accumulate([1,1,1,1,2]))
[1, 2, 3, 4, 6]