code: def parse_qs(self, qs):
          
          qs_state = urllib2.urlparse.parse_qs(qs)
          ret = {}
          for qs_var, qs_value_list in qs_state.items():
              if len(qs_value_list) > 1:
                  return None
  
              ret[qs_var] = qs_value_list[0]
  
          return ret
docs: Parse query string, but enforce one instance of each variable.
          Return a dict with the variables on success
          Return None on parse error