Output doesn't appear on standard output in Python when writing in try... except: block

Question

import urllib2
import webbrowser
import time
import sys

URL = "http://nonexisting"

while True:
    try:
        website = urllib2.urlopen(URL, timeout=1)

        if website:
            webbrowser.open_new(URL)
            break

    except KeyboardInterrupt:
        break

    except:
        sys.stdout.write('.')
        time.sleep(1)

I expect this code to write out a dot every second, but instead nothing is happening and when I press CTRL-C I get this output:

^C..........Traceback (most recent call last):
  File "stackoverflow_question.py", line 21, in <module>
    time.sleep(1)
KeyboardInterrupt

So every dot appear after the interrupt. Why is that ? How can I reach the expected result ? I tried with print statement either with the same result. On OS X and linux too.

score 3 · Accepted Answer · edited May 23 '17 at 11:43

3

You did not flush the buffer, so the output did not actually happen; it's stored somewhere in limbo.

After you interrupt, the buffer gets flushed.

See these links for more information:

Disable output buffering

How to flush output of Python print?

Also, quote from mgilson from the comment:

this code will spend most of it's time in time.sleep. During that interval, the KeyboardInterrupt won't get caught.

edited May 23 '17 at 11:43

Community

1
1

answered May 16 '13 at 23:05

zw324

26,764
16
85
118

2

Also, this code will spend most of it's time in `time.sleep`. During that interval, the `KeyboardInterrupt` won't get caught. – mgilson May 16 '13 at 23:07
indeed ! But the program is interrupted anyway :D So how can I catch it and handle it properly ? – kissgyorgy May 16 '13 at 23:15
1

@Walkman: move the while into the try. For a fuller answer, ask a new question. – SingleNegationElimination May 17 '13 at 00:05

score 0 · Answer 2 · answered May 16 '13 at 23:07

0

Did you try using print istead of sys.stdout.write?

print '.'

answered May 16 '13 at 23:07

Dory Zidon

10,497
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Output doesn't appear on standard output in Python when writing in try... except: block

2 Answers2