code: def config_string(self):
          
          return (gc.CONFIG_STRING_SEPARATOR_SYMBOL).join(
              [u"%s%s%s" % (fn, gc.CONFIG_STRING_ASSIGNMENT_SYMBOL, self.data[fn]) for fn in sorted(self.data.keys()) if self.data[fn] is not None]
          )
docs: Build the storable string corresponding
          to this configuration object.
  
          :rtype: string