from urlparse import urlparse

 def optvalue(alist, key, default=[]):
   if key in alist:
     return alist[key]
   return default

 def domain(url):
   return urlparse(url).netloc

 def join(tags):
   return "|".join(['//'+tag for tag in tags])

 def relevance(kds, wds):
   if len(kds) == 0 or len(wds) == 0:
     return 0
   return reduce(lambda acc, kw: float(wds.count(kw)) + acc, kds, 0)/len(kds + wds)

 def is_absurl(url):
   return reduce(lambda acc, p: url.startswith(p) or acc, [u'http://', u'https://', u'//'], False)