How to test a URL request in a "while True" loop

[samwyse]

On Dec 30, 10:00 am, Brian D <brianden... at 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.