Python抛出IndexError：列表索引超出范围，使用CSV

Question

I have had an error in a Python program when trying to read a CSV file. What is most perplexing is the error was not there initially, and has "come and gone" once before, but has now returned. The program is simple and the source CSV file has not been altered at any time. Here is the relevant snippet...

  with open('/home/rob/Applications/Ambient/timings.csv', 'rt') as csvfile:
  fr = csv.reader(csvfile, delimiter=',', quotechar='|')
  for row in fr:
    previous=delay
    delay=0
    millis = int(row[1])

The CSV file has this structure:

0,824 
1,496 
0,356 
1,792 
0,388 
0,764 
1,560 
0,1264 
1,724 
0,2820 
1,496 
for ~88k lines

This is the error that is thrown:

Traceback (most recent call last): File "/home/rob/Applications/Ambient/AmbientDecode_02.py", line 82, in millis = int(row[1]) IndexError: list index out of range

As you can see the accessing of the row[1] occurs early in the program after setting up the access to the CSV, and initially it did not cause an error. When the error arose later on, I definitely had not altered either that part of the Python code, or the CSV file. To pass the time I began work on some code further on, and suddenly the program began to run again. Now it has stopped again, and the same index error has returned. If I add print row after the millis = int(row[1]) the program runs???

I need a definitive answer, as I can't go on just fiddling with subsequent code and hoping somehow I fix code that I have no idea why it has crashed???

Any ideas?

Rob

Answer 1

What the error means is that, in one of the subsequent ~88k lines there is no comma and second data following the comma. You can modify the program to handle the error gracefully, thus:

with open('/home/rob/Applications/Ambient/timings.csv', 'rt') as csvfile:
    fr = csv.reader(csvfile, delimiter=',', quotechar='|')
        for row in fr:
            previous=delay
            delay=0
            try:
                millis = int(row[1])
            except IndexError:
                pass

The above code would just ignore the line where it can not find the second data (following the comma) and continues to the next line. You could instead define what needs to be done in such a scenario, by replacing pass in the above code with that logic.