Fully handling exceptions.

[Skip Montanaro]

    Jordan>     try:
    Jordan>       src_in = urllib.urlopen(ag_url)
    Jordan>     except IOError:
    Jordan>       print '%s : connection cannot be made or \
    Jordan>              server returned error.' %(ag_url)
    Jordan>     except:
    Jordan>       print '%s : unknown error.' %(ag_url)

    Jordan>   urllib's manual documents IOError as the only possible
    Jordan>   exception raised by urlopen; does this make my last except
    Jordan>   superfluous, or can there be other exceptions raised when
    Jordan>   urlopen is called that the last except may handle?

If you happen to hit Ctrl-C while urllib.urlopen is executing, you can get a
KeyboardInterrupt.  That's not strictly speaking something that urllib can
catch, but probably an interrupt you don't want to catch quite the way you
do.  How about

    try:
      src_in = urllib.urlopen(ag_url)
    except IOError:
      print '...'
    except KeyboardInterrupt:
      raise
    except:
      print '%s : unknown error.' %(ag_url)

Also, if you do catch an unexpected exception, you might well want to
display it.  See the docs for sys.get_exc_info().

-- 
Skip Montanaro (skip at pobox.com)
http://www.mojam.com/
http://www.musi-cal.com/