code: def http_url_exists(url):
      
      class HEADRequest(Request):
          def get_method(self):
              return "HEAD"
      try:
          response = urlopen(HEADRequest(url))
          return True
      except URLError:
          return False
docs: Returns whether the given HTTP URL 'exists' in the sense that it is returning
      an HTTP error code or not. A URL is considered to exist if it does not return
      an HTTP error code.