我无法理解这个封闭功能

Question

why kubik() can be called?

def funtionsaufsummerier_fabrik(x):
    def funktionaufsummerier(n):
        return sum([x(i) for i in range (1, n+1)])
    return funktionaufsummerier

i cannot understand the function above. x = kubik or x= kubik()? and when i run this code on python tutor, def funktionaufsummerier(n): is run first. But i think, funtionsaufsummerier_fabrik(x) will jump straight to return and then return def funktionaufsummerier(n):

def kubik(i):
    return i*i*i

def quadrat(i):
    return i*i


kubiksumme = funtionsaufsummerier_fabrik(kubik)
quadratsumme = funtionsaufsummerier_fabrik(quadrat)

print(kubiksumme(4))

Answer 1

funtionsaufsummerier_fabrik is a function that builds another function, returning that construction. Yes, x is a function reference. The inner function will call x on each value in the indicated range, returning the sum of those powers.

kubiksumme is a constructed function to sum cubes; quadratsumme is a constructed function to sum squares. When you call kubiksumme(4) , the effect will be

    return sum([kubik(i) for i in range (1, 4+1)])

Does that clear up the functions for you?