On Dec 30, 10:00 am, Brian D <brianden...@gmail.com> wrote:
> 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.
There, I've condensed your question to what you really meant to say.
You have several approaches. First, let's define some useful objects:
>>> max_attempts = 5
>>> def do_something(i):
assert 2 < i < 5
Getting back to original question, if you want to limit the number of
attempts, don't use a while, use this:
>>> for count in xrange(max_attempts):
print 'attempt', count+1
do_something(count+1)
attempt 1
Traceback (most recent call last):
File "<pyshell#55>", line 3, in <module>
do_something(count+1)
File "<pyshell#47>", line 2, in do_something
assert 2 < i < 5
AssertionError
If you want to keep exceptions from ending the loop prematurely, you
add this:
>>> for count in xrange(max_attempts):
print 'attempt', count+1
try:
do_something(count+1)
except StandardError:
pass
Note that bare except clauses are *evil* and should be avoided. Most
exceptions derive from StandardError, so trap that if you want to
catch errors. Finally, to stop iterating when the errors cease, do
this:
>>> try:
for count in xrange(max_attempts):
print 'attempt', count+1
try:
do_something(count+1)
raise StopIteration
except StandardError:
pass
except StopIteration:
pass
attempt 1
attempt 2
attempt 3
Note that StopIteration doesn't derive from StandardError, because
it's not an error, it's a notification. So, throw it if and when you
want to stop iterating.
BTW, note that you don't have to wrap your code in a function.
do_something could be replaced with it's body and everything would
still work.
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