Just check a google server
except urllib2.URLError as err: pass
188.8.131.52 is one of the IP-addresses for google.com. Change http://184.108.40.206 to whatever site can be expected to respond quickly.
Using a numerical IP-address avoids a DNS lookup,
which may block the urllib2.urlopen call for more than a second. Thanks to @rzetterberg for pointing this out.
By specifying the timeout=1 parameter, the call to urlopen will not take much longer than 1 second even if the internet is not “on”.