Python-变量如何影响循环

Question

I am wondering why there is a different result when I change from arr[n] in version 1 to n in version 2:

Version 1

def summer_69(arr):
    list_sum2 = 0
    n = 0
    for arr[n] in range(arr[n] == 6, (arr[n]== 9) + 1):
            list_sum2 += arr[n]
    print(list_sum2)

summer_69([1, 3, 5])
summer_69([4, 5, 6, 7, 8, 9])

Result for Version 1

0
0

Version 2

def summer_69(arr):
    list_sum2 = 0
    n = 0
    for n in range(arr[n] == 6, (arr[n]== 9) + 1):
            list_sum2 += arr[n]
    print(list_sum2)

summer_69([1, 3, 5])
summer_69([4, 5, 6, 7, 8, 9])

Result for Version 2

1
4

Answer 1

that's not how range works.

in this line:

for n in range(arr[n] == 6, (arr[n]== 9) + 1):

arr[n] == 6 and (arr[n]== 9) + 1 are returning truth values because == is a comparison operator so n here at best takes values 0 or 1.

you want

for n in range(6, 10):

so that the value of n iterates from 6 to 9, range() being inclusive to the left and exclusive to the right