I second the background running feature.

This should work.
first of all, long url should be url-quoted.
then bitly api returns json data so needs json module to load.
build a urllib2 opener to open formatted <code>bitly_url</code>, that's it.

<pre>
import clipboard
import urllib2
import json

kurzurl = urllib2.quote(clipboard.get())

def shorten_url(long_url):
username = 'username'
apikey = 'apikey'
bitly_url = "http://api.bit.ly/v3/shorten?login=%s&apiKey=%s&longUrl=%s" %(username, apikey, long_url)
r = urllib2.Request(bitly_url)
opener = urllib2.build_opener()
f = json.loads(opener.open(r).read())
short_url = f['data']['url']
return short_url

print shorten_url(kurzurl)
</pre>