python中怎么倒着遍历字符串?

Question

codecademy上过教程.练习中遇到了题述问题.且不能用reversed函数跟[::-1]
大家有什么好方法?

Answer 1

双端队列

from collections import deque


def string_reverse(string):
    d = deque()
    d.extendleft(string)
    return ''.join(d);

Answer 2

def rev(s):
    r = list()
    for c in s:
        r.insert(0, c)
    return ''.join(r)

Answer 3

str = "hello world"
l = len(str)
for i in range(l):
    print str[l - i - 1]

Answer 4

def reserveStr(s):
    length = len(s)
    result = ''
    for i in range(length):
        result += s[length - i - 1]
    return result
        

Answer 5

def reversed_index(n):
    for i in range(n-1, -1, -1):
        yield i


test_string = "我爱北京天安门"
new_string = ""
for i in reversed_index(len(test_string)):
    new_string += test_string[i]
print(new_string)