def __setattr__(self, key, val):
        prefix = object.__getattribute__(self, "prefix")
        if prefix:
            prefix += "."
        prefix += key
        # you can't set new keys
        # can you can't overwrite subtrees
        if key in self.d and not isinstance(self.d[key], dict):
            _set_option(prefix, val)
        else:
            raise OptionError("You can only set the value of existing options")
dataset/ETHPy150Open cloudera/ibis/ibis/config.py/DictWrapper.__setattr__/original