如何修复IndexError：Python中的字符串索引超出范围

Question

My code returns

IndexError: string index out of range

The code is supposed to make a string be split into groups of two and inserted into a list but instead returns Error

def tokenize(tokenlist):
    newList = [] 
    for i in range(1,6,2):
        newList.append(tokenlist[i]+tokenlist[i+1])
    return newList

The input is "abcdef" and the output I expected was the list ["ab","cd","ef"] but I got an error. How do I get my code to do what I intended?

Answer 1

Your input is of length 6 so last index is 5

Your range goes up to 5

So i+1 in tokenlist[i+1] goes up to 6 which causes the IndexError as lists and strings are indexed from 0 in python

Correct to range(0,6,2)

Better yet, use len(tokenlist) instead of 6.

Be aware that if it is odd you will get an error. You should specify expected behavior in this case.

For instance, if last character may be alone use string slicing:

def tokenize(tokenlist):
    newList = []
    for i in range(0, len(tokenlist), 2):
        newList.append(tokenlist[i: i + 2])
    return newList

In any case, as commented, you should refactor your code according to python guidelines. For instance

def tokenize(tokenlist):
    newList = []
    for i in range(0, len(tokenlist), 2):
        newList.append(tokenlist[i] + tokenlist[i + 1])
    return newList

Answer 2

Look at the call to range( 1, 6, 2 ) .
What will happen when i = 5 ?

This will have the code trying to make an element of tokenlist[5] and tokenlist[6] , whereas when working on "abcdef" , there are only elements tokenlist[0] (a) to tokenlist(5) (f).

So this element in the range is off the end of the list.

BTW: What should this function do when len( tokenlist ) is an odd number?