p>

  try：
 outrank2 = outlist [2] [outlist [2] .index（'：'）+ 1：] 
除了ValueError：
 outrank2 =？
 

I am running an external function which should return a string - sometimes, however, this function fails and the string is empty. The behaviour I would like is "if the string is empty(i.e a value error will occur) instead print a '?' string to my CSV).

Here is my code :

    outlist = output.split('\r\n') #splitting the string
    outrank1 = outlist[1][outlist[1].index(':')+1:]
    outrank2 = outlist[2][outlist[2].index(':')+1:]
    print outrank1
    print outrank2
    print str(outlist[0])
    print str(outlist[1])
    print str(outlist[2])
    csvout.writerow([str(outlist[0]), str(outrank1), str(outrank2)]) #writing,error here 

Here is a sample of the bug I am encountering :

Traceback (most recent call last):
  File "Methods.py", line 24, in <module>
    outrank2 = outlist[2][outlist[2].index(':')+1:]
ValueError: substring not found

In this case, instead of an error I would like to save a '?' in outrank2. How can I do this?

you could wrap that in a try-except

try:
  outrank2 = outlist[2][outlist[2].index(':')+1:]
except ValueError:
  outrank2 = "?"