pipelined generator

[Gribouillis]

is there any guide about deque?

Deque is only a type in the standard library. It is documented here. You could also read this.

However, the expression I used above

item = deque(iterable, maxlen=1)[-1]

is only a trick to obtain the last element of a non empty iterable. You could replace it with a loop

for item in iterable:
    pass