如何在Python的while循环中修复此错误？

Question

I have a list in Python, list1 , and the following while loop:

j = 0
while list1[j] >= list1[j - 1] and j < len(list1):
    # do something here and return k
    # k is always incremented
    j += k

I got the following error: IndexError: string index out of range

How to fix this error?

Answer 1

You need to start your while condition with the length check. Python short-circuits the operations in your while loop, so when j is too large, it will just throw an error rather than gracefully ending the loop. So like this:

while j < len(list1) and list1[j] >= list1[j - 1]:

Your first iteration of the loop is comparing list1[0] and list1[-1] , which is valid , but may not be what you want to be doing (it compares the first and last elements of list1 ). Depending on your goals, you may or may not wish to start your loop with j = 1 .

Answer 2

When using an and , if the first condition is false, the second is not even checked. Simply use:

j = 0
while j < len(list1) and list1[j] >= list1[j - 1]:
    # do something here and return k
    # k is always incremented
    j += k