Python: Continue looping after exception

Question

I have the following script (below). which will return the status code of URLs. It loops through a file and tries to connect to each host. Only problem is that it obviously stops looping when it reaches an exception.

I have tried numerous things to put the how of it in a loop, but to no avail. Any thoughts?

import urllib
import sys
import time

hostsFile = "webHosts.txt"


try:
    f = file(hostsFile)
    while True:
        line = f.readline().strip()
        epoch = time.time()
        epoch = str(epoch)
        if len(line) == 0:
            break
        conn = urllib.urlopen(line)
        print epoch + ": Connection successful, status code for " + line + " is " + str(conn.code) + "\n"
except IOError:
    epoch = time.time()
    epoch = str(epoch)
    print epoch + ": Connection unsuccessful, unable to connect to server, potential routing issues\n"
    sys.exit()
else:
    f.close()

EDIT:

I've come up with this in the mean-time, any issues with this? (i'm still learning :p )...

f = file(hostsFile)
while True:
    line = f.readline().strip()
    epoch = time.time()
    epoch = str(epoch)
    if len(line) == 0:
        break
    try:
        conn = urllib.urlopen(line)
        print epoch + ": Connection successful, status code for " + line + " is " + str(conn.code) + "\n"
    except IOError:
        print epoch + "connection unsuccessful"

Thanks,

MHibbin

Have you tried catching the exception using a try...except block, and then warning and continuing? — Alex Wilson
– Alex Wilson, Commented Jul 3, 2012 at 8:17
@Alex Wilson, I had another play around... and changed my question... is this what you meant? — MHibbin
– MHibbin, Commented Jul 3, 2012 at 8:20

aychedee · Accepted Answer · 2012-07-03 08:46:26Z

16

You could handle the exception where it is raised. Also, use a context manager when opening files, it makes for simpler code.

with open(hostsFile, 'r') as f:
    for line in f:
        line = line.strip()
        if not line:
            continue

        epoch = str(time.time())

        try:
            conn = urllib.urlopen(line)
            print epoch + ": Connection successful, status code for " + line + " is " + str(conn.code) + "\n"
        except IOError:
            print epoch + ": Connection unsuccessful, unable to connect to server, potential routing issues\n"

edited Jul 3, 2012 at 8:46

answered Jul 3, 2012 at 8:21

aychedee

25.7k8 gold badges82 silver badges83 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

MHibbin Over a year ago

I came to the same conclusion just after I posted the question . :-) Thanks for confirming What I had done.

georg Over a year ago

for line in f is probably better here than a while loop.

aychedee Over a year ago

Absolutely, and if you test each line against the empty string (line == '':) before stripping the newlines (\n) then you can handle blank lines in the source file without exiting prematurely.

martineau Over a year ago

@H. Dunlop: if line: or if not line: continue

MHibbin Over a year ago

@H.Dunlop, Thanks I have list of approx 100 urls to test (for internal network connectivity purposes (they are appliances with webUI). We would like to check them every 60 seconds. is it possible to speed this process up... can I use this script to generate a small script for each host (or would that be bad for performance)

|

Rohan · Accepted Answer · 2012-07-03 08:18:06Z

4

You need to handle exception raised by urllib.urlopen(line), something like this.

try:
    f = file(hostsFile)
    while True:
        line = f.readline().strip()
        epoch = time.time()
        epoch = str(epoch)
        if len(line) == 0:
            break
        try:
           conn = urllib.urlopen(line)
        except IOError:
           print "Exception occured"
           pass
except IOError:
    epoch = time.time()
    epoch = str(epoch)
    print epoch + ": Connection unsuccessful, unable to connect to server, potential routing issues\n"
    sys.exit()
else:
    f.close()

answered Jul 3, 2012 at 8:18

Rohan

53.5k12 gold badges95 silver badges89 bronze badges

1 Comment

MHibbin Over a year ago

Thanks for the answer. I've edited my question with a possible solution I found in the mean time.

JRajan · Accepted Answer · 2012-07-03 09:00:03Z

1

You could try catching the exception inside the while loop as something like this.

try:
    f = file(hostsFile)
    while True:
        line = f.readline().strip()
        epoch = time.time()
        epoch = str(epoch)
        if len(line) == 0:
            break
        try:
            conn = urllib.urlopen(line)
            print epoch + ": Connection successful, status code for " + line + " is " + str(conn.code) + "\n"
        except:
            epoch = time.time()
            epoch = str(epoch)
            print epoch + ": Connection unsuccessful, unable to connect to server, potential routing issues\n"
except IOError:
    pass
else:
    f.close()

answered Jul 3, 2012 at 9:00

JRajan

7024 silver badges20 bronze badges

Collectives™ on Stack Overflow

Python: Continue looping after exception

3 Answers 3

6 Comments

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

6 Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related