python IndexError：字符串索引超出范围

Question

I'm getting the IndexError: string index out of range. Each line in the file "document_words" ends with "-99". So i think error may be because "-99" is not converted to int. But i'm not sure. If that is the case how can i convert "-99" to int and break from the loop.

Following is my code:

words=open('words','r')
image=open('document_words','r')
data=open('input','a')

linecount=0

for line in image:
    if line.strip():
        linecount+=1

image.read()
image.seek(0,0)
while linecount>0:
    line1=image.readline().split()
    for entry in line1:
        num=int(entry)
        if (num<0):
            print("break from loop")
            break
        else:
            tag=words.readline()[num]
            data.write(str(tag)+' ')
    data.write('\n')
    linecount=linecount-1

data.flush()
data.close()
words.close()
image.close()

Answer 1

You haven't told us which line fails, but this looks like the obvious one

tag = words.readline()[num]

so num is outside the bounds. I don't think it is the -99 because it should break in that case. You can add a try/except to help track it down

try:
    tmp = words.readline()
    tag = tmp[num]
except IndexError, e:
    print tmp, num

EDIT: Looks like you are mixing tabs and spaces for the indenting. This is a no-no unless you are using 8 character tab-stops