code: def get_new_locations(self, urls):
          
          seen = set(urls)
          for i in urls:
              for k in self.get_locations(i):
                  if k not in seen:
                      seen.add(k)
                      yield k
docs: Get valid location header values for all given URLs.
  
          The returned values are new, that is: they do not repeat any
          value contained in the original input. Only unique values
          are yielded.
  
          :param urls: a list of URL addresses
          :returns: valid location header values from responses
          to the URLs