list index error from regex

Question

I have following function that gives me errors. It should extract the IP from the website url Sometimes it works sometimes i get following error:

File "test.py", line 30, in getIPextA
address = grab[0]                    # get address as a string
IndexError: list index out of range

Function:

def getIPextA():
"""
Version A Get external ip from "http://checkip.dyndns.org/"
"""
site=geturldata("http://checkip.dyndns.org/")
if site =="" : return [0,0,0,0]
grab = re.findall('\d{2,3}.\d{2,3}.\d{2,3}.\d{2,3}',site)
address = grab[0]                    # get address as a string
return map(int,address.split('.'))   # as an integer list

geturldata() gets all the data from the url page as a long string with some error checking if the url fails etc... — tubos
– tubos, Commented Oct 26, 2014 at 10:00

user3094403 · Accepted Answer · 2014-10-26 09:22:40Z

1

You get the error when the IP address could not match the regex. The reason is probably that you sometimes have an IP containing a one-digit part. These are also valid IPs. You should also escape the dot, because a dot in a regex means that it can match any char.

grab = re.findall('\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}',site)

answered Oct 26, 2014 at 9:22

user3094403

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Comments

Borodin · Accepted Answer · 2014-10-26 09:39:04Z

0

I suggest something like this instead

    match = re.search(r' (\d{1,3}) \. (\d{1,3}) \. (\d{1,3}) \. (\d{1,3}) ', site, flags=re.X)
    return match.groups() if match else [0, 0, 0, 0]

which allows between one and three digits in each octet, and has the dots . escaped properly as well. The flags parameter allows me to add insignificant whitespace so that the regex is more readable. Each octet is cointained in parentheses, so the MatchObject will return a list of four decimal strings if you call its groups method.

But I don't know what your geturldata function is so I can't help any more.

answered Oct 26, 2014 at 9:39

Borodin

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