为什么使用 while 循环可以使程序工作，但我原来的 for 循环不起作用？ (DNA pset6)

Question

刚刚完成 pset6 DNA，但我很困惑。在计算连续的 dna 序列时，如果我使用 for 循环遍历 dna 序列文本，我的代码将始终产生“不匹配”作为输出，但如果我将其更改为 while 循环以遍历 dna 序列它会工作。我不知道为什么。我在 while 循环部分下方注释掉了整个 for 循环部分。

任何帮助表示赞赏。

from sys import argv, exit
import csv

if len(argv) != 3:
    print("Usage: python dna.py data.csv sequence.txt")
    exit(1)

with open(argv[1], 'r') as csv_file:
    csv_reader = csv.reader(csv_file)
    for row in csv_reader:
        header = row
        header.pop(0)
        break

dictionary = {}

for item in header:
    dictionary[item] = 0

with open(argv[2], 'r') as dna_txt:
    dna_reader = dna_txt.read()

# This iteration using while loop works 
for key in dictionary:
    temp = 0 
    max_count = 0
    i = 0
    # This while loop works
    while i < len(dna_reader):
        if dna_reader[i : i + len(key)] == key:
            temp += 1
            if ((i + len(key)) < len(dna_reader)):
                i += len(key)
                continue
        else:
            if temp > max_count:
                max_count = temp
            temp = 0
        i += 1
    dictionary[key] = max_count

# This iteration does not work, only difference is for loop instead of while loop, why is that? Commented out so it doesn't interfere
'''for key in dictionary:
    temp = 0 
    max_count = 0

    # This for loop does not work

    for i in range(len(dna_reader)):
        if dna_reader[i : i + len(key)] == key:
            temp += 1
            if ((i + len(key)) < len(dna_reader)):
                i += len(key)
                continue
        else:
            if temp > max_count:
                max_count = temp
            temp = 0
    dictionary[key] = max_count'''

with open(argv[1], 'r') as file:
    table = csv.DictReader(file)
    for person in table:
        count = 0
        for dna in dictionary:
            if int(dictionary[dna]) == int(person[dna]):
                count += 1
            else:
                count = 0
            if count == len(header):
                print(person['name'])
                exit(1)

print('No match')
exit(0)

Answer 1

我能看到的唯一实质性区别是i += len(key) 的效果。在 for 循环中，i 变量将在每个循环开始时重新实例化。因此，这种说法没有实际效果。在while循环的情况下，相同的i变量被重用。

考虑这个例子：

for i in range(10):
    print(i)
    if i == 5:
        i += 2

这个输出将是：

0
1
2
3
4
5
6
7
8
9

希望这会有所帮助。