如何修复Python中的“ IndexError：字符串索引超出范围”错误

Question

我最近开始在Coursera的MOOC上学习Python。 我正在尝试编写一个while循环，该循环从字符串的最后一个字符开始，向后移动到字符串的第一个字符，将每个字母打印在单独的行上，除了向后。

我已经写了代码，可以给我想要的输出，但是也给我一个错误

“ IndexError：字符串索引超出范围”

index = 0
fruit = "potato"
while index <= len(fruit) :
    index = index - 1
    letter = fruit[index] 
    print(letter)

  Traceback (most recent call last): File "strings_01.py", line 8, in <module> letter = fruit[index] IndexError: string index out of range 

Answer 1

尝试使用其他while循环条件：

index = 0
fruit = "potato"
while abs(index) < len(fruit):
    index = index - 1
    letter = fruit[index] 
    print(letter)

Answer 2

这将起作用。 当然，这只是为了学习，在Python中有更好的方法可以做到这一点。

fruit = "potato"
index = len(fruit) -1 #Python indexes starts from 0!
while index >= 0 :
    letter = fruit[index]
    print(letter)
    index -= 1 #decrease at the END of the loop!

输出：

o
t
a
t
o
p

Answer 3

fruit = "potato"
index = len(fruit)
while index > 0 :
    index = index - 1
    letter = fruit[index] 
    print(letter)

Answer 4

尝试这个：

>>> fruit = "potato"
>>> fruit = fruit[::-1]
>>> fruit
'otatop'
>>> for letter in fruit:
...     print(letter)
...
o
t
a
t
o
p

或者使用while loop ：

>>> fruit = "potato"
>>> fruit = fruit[::-1]
>>> fruit
'otatop'
>>>  index = 0
>>> while index < len(fruit):
...     print(fruit[index])
...     index+=1
...
o
t
a
t
o
p

Answer 5

这就是你要找的

index = 0
fruit = "potato"
while index > -(len(fruit)) :
    index = index - 1
    letter = fruit[index]
    print(letter)