It seems that accumulate keeps the previous results, whereas reduce (which is known as fold in other languages) does not necessarily.
e.g. list(accumulate([1,2,3], operator.add)) would return [1,3,6] whereas a plain fold would return 6
Also (just for fun, don’t do this) you can define accumulate in terms of reduce
def accumulate(xs, f):
return reduce(lambda a, x: a + [f(a[-1], x)], xs[1:], [xs[0]])