For Python 3, try doing this:
import urllib.request, urllib.error
url = 'http://www.google.com/qqqq'
try:
conn = urllib.request.urlopen(url)
except urllib.error.HTTPError as e:
# Return code error (e.g. 404, 501, ...)
# ...
print('HTTPError: {}'.format(e.code))
except urllib.error.URLError as e:
# Not an HTTP-specific error (e.g. connection refused)
# ...
print('URLError: {}'.format(e.reason))
else:
# 200
# ...
print('good')