Python 2.7中for循环无法递增迭代器变量的问题求助

核心问题 #

你代码里的矛盾点在于同时用while和for循环操作同一个变量，直接打乱了索引变量的逻辑：

1. 初始化的i是数值型索引，但嵌套的for i in s会把i重新赋值为字符串里的每个字符，完全覆盖了原来的数值，导致while循环的索引递增逻辑彻底失效——第一次进入while后，for循环直接遍历整个字符串，结束后i变成最后一个字符（比如hello里的o），此时while判断字符与数字的大小，结果永远为False，循环直接终止。
2. 当你把变量名改成it时，for循环结束后it是字符串的最后一个字符，此时while判断it < len(s)会触发类型错误（Python3不允许字符串和整数直接比较），导致程序崩溃，循环根本无法启动。

修正方案 #

方案1：直接用for循环遍历字符（推荐，更简洁） #

完全不需要手动维护索引，for循环本身就是逐个迭代字符串元素：

def solution(s):
    m = ""
    braille = {
        " ": "000000",
        "^": "000001",
        "a": "100000",
        "b": "110000",
        "c": "100100",
        "d": "100110",
        "e": "100010",
        "f": "110100",
        "g": "110110",
        "h": "110010",
        "i": "010100",
        "j": "010110",
        "k": "101000",
        "l": "111000",
        "m": "101100",
        "n": "101110",
        "o": "101010",
        "p": "111100",
        "q": "111110",
        "r": "111010",
        "s": "011100",
        "t": "011110",
        "u": "101001",
        "v": "111001",
        "w": "010111",
        "x": "101101",
        "y": "101111",
        "z": "101011"
    }

    for char in s:
        if char.isupper():
            m += braille["^"] + braille[char.lower()]
        else:
            m += braille[char]
    print(m)

solution("hello")

方案2：用while手动维护索引 #

如果一定要手动控制索引递增，删除嵌套的for循环，直接通过索引取字符并手动递增：

def solution(s):
    i = 0
    m = ""
    braille = {
        " ": "000000",
        "^": "000001",
        "a": "100000",
        "b": "110000",
        "c": "100100",
        "d": "100110",
        "e": "100010",
        "f": "110100",
        "g": "110110",
        "h": "110010",
        "i": "010100",
        "j": "010110",
        "k": "101000",
        "l": "111000",
        "m": "101100",
        "n": "101110",
        "o": "101010",
        "p": "111100",
        "q": "111110",
        "r": "111010",
        "s": "011100",
        "t": "011110",
        "u": "101001",
        "v": "111001",
        "w": "010111",
        "x": "101101",
        "y": "101111",
        "z": "101011"
    }

    while i < len(s):
        char = s[i]
        if char.isupper():
            m += braille["^"] + braille[char.lower()]
        else:
            m += braille[char]
        i += 1  # 手动递增索引变量
    print(m)

solution("hello")

内容的提问来源于stack exchange，提问作者August Fercar