如何错误检查列表索引超出范围

Question

I have a read.log file that will have lines such as...

10.2.177.170 Tue Jun 19 03:30:55 CDT 2018
10.2.177.170 Tue Jun 19 03:31:03 CDT 2018
10.2.177.170 Tue Jun 19 03:31:04 CDT 2018
10.2.177.170 Tue Jun 19 03:32:04 CDT 2018
10.2.177.170 Tue Jun 19 03:33:04 CDT 2018

My code will read the 3rd to last line and combine strings. So the normal output would be:

2018:19:03:32:04

My problem is, if there are only 4 or less lines of data such as

10.1.177.170 Tue Jun 19 03:30:55 CDT 2018
10.1.177.170 Tue Jun 19 03:31:03 CDT 2018
10.1.177.170 Tue Jun 19 03:31:04 CDT 2018
10.1.177.170 Tue Jun 19 03:32:04 CDT 2018

I get an error

    x1 = line.split()[0]
IndexError: list index out of range

How can I error check this or keep it from happening? I have been trying to check how many lines there are in the log and if less than 5, print a notice. Are there better options?

def run():

    f = open('read.log', 'r')
    lnumber = dict()
    for num,line in enumerate(f,1):  
        x1 = line.split()[0]
        log_day  = line.split()[3]
        log_time = line.split()[4]
        log_year = line.split()[6]
        if x1 in lnumber:
            lnumber[x1].append((log_year + ":" + log_day + ":" + log_time))
        else:
            lnumber[x1] = [(num,log_time)]

    if x1 in lnumber and len(lnumber.get(x1,None)) > 2:

        # if there are less than 3 lines in document, this will fail

        line_time = (lnumber[x1][-3].__str__())
        print(line_time)
    else:
        print('nothing')
    f.close

run()

Answer 1

f.readlines() gives you a list of lines in a file. So, you could try reading in all the lines in a file:

f = open('firewall.log', 'r')
lines = f.readlines()

And exiting if there are 4 or less lines:

if len(lines) <= 4:
    f.close()
    print("4 or less lines in file")
    exit()

That IndexError you're getting is because you're calling split() on a line with nothing on it. I would suggest doing something like if not line: continue to avoid that case.