Keep getting string index out of range error in code

Question

I keep getting the IndexError: string index out of range, and am wondering what I'm doing wrong with the code.

inFile=open('pa7.cards','r')
cardnum=inFile.readline().strip()

def main():
    while cardnum!='99999':
        Step1(cardnum)
def CheckLen(num):
    if len(num)>=13 and len(num)<=16:
        return True
    else:
        return False
def Step1(num):
    total=0
    for i in range(len(num)-2,0,-2):
        if eval(num[i]*2)>=10:
            i=eval(num[i])*2
            i=str(i)
            i=eval(i[0])+eval(i[1])
            total+=i
        else:
            total+=i
    return total
def Step2(num):
    total=0
    for i in range(len(num)-1,0,-2):
        total+=i
    return total
def Step3(num):
    total=Step1(num)+Step2(num)
    if total%10==0:
        return True
    else:
        return False
##def DetermineType(num):
main()

This is what the input file looks like:

4388576018402626 
4388576018410707 
37271983 
99999

This is the error:

Traceback (most recent call last):
  File "C:/Users/Andrew/Desktop/pa7.py", line 47, in <module>
    main()
  File "C:/Users/Andrew/Desktop/pa7.py", line 18, in main
    Step1(cardnum)
  File "C:/Users/Andrew/Desktop/pa7.py", line 30, in Step1
    i=eval(i[0])+eval(i[1])
IndexError: string index out of range

Yeah...just say that you could use int() instead of eval(). However, never use eval(). About that error, i = int(i[0])+int(i[1]) I think i's length is 1 so you can't do something like i[1]. — Remi Guan
– Remi Guan, Commented Nov 11, 2015 at 10:02
Agree with Kevin. For i<10 str(i) will generate string length one which then causes the error in i[1] — 576i
– 576i, Commented Nov 11, 2015 at 10:03

Tim Pietzcker · Accepted Answer · 2015-11-11 10:01:40Z

1

You're doing a few Bad Things^TM there.

The source of your error is that i is built by taking a digit from your "number string", doubling it and converting it back to a string (so "8" becomes "16").

Then you try and access i[1] - which is out of range if i is only 1 character long.

But there are more problems - reusing the name i within the for loop, using eval() (shudder!) where int() would do, iterating over a string using range() instead of slices...

For example,

for i in range(len(num)-2,0,-2):

should be

for digit in num[-2:0:-2]:

answered Nov 11, 2015 at 10:01

Tim Pietzcker

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1 Comment

52655841856 Over a year ago

okay so im not to strong in slices yet, but i've tried to make changes to the code, this is what i did, though it just gives me an infinite loop:

52655841856 · Accepted Answer · 2015-11-11 10:38:26Z

0

def Step1(num):
    total=0
    for digit in num[-2:0:-2]:
        digit=int(digit)

        if int(num[digit])*2>=10:
            x=int(num[digit])*2
            x1=str(x)
            x2=int(x1[0])+int(x1[1])
            total+=x2
        else:
            x=int((num[digit]))
            total+=x
    return total

answered Nov 11, 2015 at 10:38

52655841856

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