On Dec 30, 2009, at 11:00 AM, Brian D wrote:
I'm actually using mechanize, but that's too complicated for testing
purposes. Instead, I've simulated in a urllib2 sample below an attempt
to test for a valid URL request.
I'm attempting to craft a loop that will trap failed attempts to
request a URL (in cases where the connection intermittently fails),
and repeat the URL request a few times, stopping after the Nth attempt
is tried.
Specifically, in the example below, a bad URL is requested for the
first and second iterations. On the third iteration, a valid URL will
be requested. The valid URL will be requested until the 5th iteration,
when a break statement is reached to stop the loop. The 5th iteration
also restores the values to their original state for ease of repeat
execution.
What I don't understand is how to test for a valid URL request, and
then jump out of the "while True" loop to proceed to another line of
code below the loop. There's probably faulty logic in this approach. I
imagine I should wrap the URL request in a function, and perhaps store
the response as a global variable.
This is really more of a basic Python logic question than it is a
urllib2 question.
Hi Brian,
While I don't fully understand what you're trying to accomplish by
changing the URL to google.com after 3 iterations, I suspect that some
of your trouble comes from using "while True". Your code would be
clearer if the while clause actually stated the exit condition. Here's
a suggestion (untested):
MAX_ATTEMPTS = 5
count = 0
while count <= MAX_ATTEMPTS:
count += 1
try:
print 'attempt ' + str(count)
request = urllib2.Request(url, None, headers)
response = urllib2.urlopen(request)
if response:
print 'True response.'
except URLError:
print 'fail ' + str(count)
You could also save the results (untested):
MAX_ATTEMPTS = 5
count = 0
results = [ ]
while count <= MAX_ATTEMPTS:
count += 1
try:
print 'attempt ' + str(count)
request = urllib2.Request(url, None, headers)
f = urllib2.urlopen(request)
# Note that here I ignore the doc that says "None may be
# returned if no handler handles the request". Caveat emptor.
results.append(f.info())
f.close()
except URLError:
# Even better, append actual reasons for the failure.
results.append(False)
for result in results:
print result
I guess if you're going to do the same number of attempts each time, a
for loop would be more expressive, but you probably get the idea.
Hope this helps
Philip
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