code: def check_is_undeclared(self, id_, lineno, classname='identifier',
                              scope=None, show_error=False):
          
          result = self.get_entry(id_, scope)
          if result is None or not result.declared:
              return True
  
          if scope is None:
              scope = self.current_scope
  
          if show_error:
              syntax_error(lineno,
                           'Duplicated %s "%s" (previous one at %s:%i)' %
                           (classname, id_, self.table[scope][id_].filename,
                            self.table[scope][id_].lineno))
          return False
docs: The reverse of the above.
  
          Check the given identifier is not already declared. Returns True
          if OK, False otherwise.