code: def set_default(self, name, value):
      
      fl = self._flags()
      if name not in fl:
        self._set_unknown_flag(name, value)
        return
      fl[name]._set_default(value)  # pylint: disable=protected-access
      self._assert_validators(fl[name].validators)
docs: Changes the default value of the named flag object.
  
      The flag's current value is also updated if the flag is currently using
      the default value, i.e. not specified in the command line, and not set
      by FLAGS.name = value.
  
      Args:
        name: str, the name of the flag to modify.
        value: The new default value.
  
      Raises:
        UnrecognizedFlagError: Raised when there is no registered flag named name.
        IllegalFlagValueError: Raised when value is not valid.