Hi,
I have been using Java/Perl professionally for many years and have been trying
to learn python3 recently. As my first program, I tried writing a class for a
small project, and I am having really hard time understanding exception
handling in urllib and in python in general...
Basically, what I want to do is very simple, try to fetch something
"tryurllib.request.urlopen(request)", and:
- If request times out or connection is reset, re-try n times
- If it fails, return an error
- If it works return the content.
But, this simple requirement became a nightmare for me. I am really confused
about how I should be checking this because:
- When connection times out, I sometimes get URLException with "reason" field
set to socket.timeout, and checking (isinstance(exception.reason,
socket.timeout)) works fine
- But sometimes I get socket.timeout exception directly, and it has no
"reason" field, so above statement fails, since there is no reason field there.
- Connection reset is a totally different exception
- Not to mention, some exceptions have msg / reason / errno fields but some
don't, so there is no way of knowing exception details unless you check them
one by one. The only common thing I could was to find call __str__()?
- Since, there are too many possible exceptions, you need to catch
BaseException (I received URLError, socket.timeout, ConnectionRefusedError,
ConnectionResetError, BadStatusLine, and none share a common parent). And,
catching the top level exception is not a good thing.
So, I ended up writing the following, but from everything I know, this looks
really ugly and wrong???
try:
response = urllib.request.urlopen(request)
content = response.read()
except BaseException as ue:
if (isinstance(ue, socket.timeout) or (hasattr(ue, "reason") and
isinstance(ue.reason, socket.timeout)) or isinstance(ue, ConnectionResetError)):
print("REQUEST TIMED OUT")
or, something like:
except:
(a1,a2,a3) = sys.exc_info()
errorString = a2.__str__()
if ((errorString.find("Connection reset by peer") >= 0) or
(errorString.find("error timed out") >= 0)):
Am I missing something here? I mean, is this really how I should be doing it?
Thanks.
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