在cod中不断获取字符串索引超出范围错误

Question

我一直在得到IndexError: string index out of range，我想知道我的代码有什么问题

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()    

输入文件如下所示：

4388576018402626 
4388576018410707 
37271983 
99999 

这是错误：

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

Answer 1

你在做一些坏事

错误的来源是i是通过从“数字字符串”中提取一个数字，将其加倍并将其转换回字符串（因此"8"变成"16"）而构建的

然后尝试访问i[1]—如果i只有1个字符长，则超出范围

但是还有更多的问题-在for循环中重用名称i，使用eval()（shubder！）其中int()就可以了，使用range()而不是切片来迭代字符串

例如

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

应该是

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

Answer 2

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