原始代码：

from typing import Dictrelated_objects_for_fetch: Dict[str, list] = {}for key, value in [('k1', 'v1'), ('k1', 'v2'), ('k2', 'v2'), ('k3', 'v3'), ('k2', 'v2')]:if key not in related_objects_for_fetch:related_objects_for_fetch[key] = []if value not in (values := related_objects_for_fetch[key]):values.append(value)for k, v in related_objects_for_fetch.items():print(k, v)

修改后：

from collections import defaultdictrelated_objects_for_fetch: defaultdict[str, list] = defaultdict(list)for key, value in [('k1', 'v1'), ('k1', 'v2'), ('k2', 'v2'), ('k3', 'v3'), ('k2', 'v2')]:if value not in (values := related_objects_for_fetch[key]):values.append(value)for k, v in related_objects_for_fetch.items():print(k, v)

少了if key not in xxx的判断，代码更加简洁。

需要注意的是：

my_dict['not-exist-key']这个会抛出KeyError

而my_defaultdict['not-exist-key']则会返回空列表

如下图：