環境

Python3.10.2
- dataclasses-json 0.5.7

何が起きた？

dataclasses-jsonのfrom_dict関数で、Dict型のプロパティに文字列を設定しようとすると、当たり前ですがエラーが発生します。

bar.py

from dataclasses import dataclass
from dataclasses_json import dataclass_json
from typing import List, Dict, Any


@dataclass_json
@dataclass
class Person:
    name: str
    type: Dict[str, Any]
    """型が間違っている。正しくは`str`型"""


@dataclass_json
@dataclass
class School:
    name: str
    people: List[Person]


d_person = {"name": "Alice", "type": "junior"}
d_school = {"name": "tokyo", "people": [d_person]}

school = School.from_dict(d_school)
print(school)

vagrant@example:~/Documents/study/python$ python bar.py
Traceback (most recent call last):
  File "/home/vagrant/.pyenv/versions/3.10.2/lib/python3.10/site-packages/dataclasses_json/core.py", line 263, in _decode_generic
    res = _get_type_cons(type_)(xs)
  File "/home/vagrant/.pyenv/versions/3.10.2/lib/python3.10/site-packages/dataclasses_json/core.py", line 317, in <genexpr>
    items = (_decode_dataclass(type_arg, x, infer_missing)
  File "/home/vagrant/.pyenv/versions/3.10.2/lib/python3.10/site-packages/dataclasses_json/core.py", line 201, in _decode_dataclass
    init_kwargs[field.name] = _decode_generic(field_type,
  File "/home/vagrant/.pyenv/versions/3.10.2/lib/python3.10/site-packages/dataclasses_json/core.py", line 254, in _decode_generic
    ks = _decode_dict_keys(k_type, value.keys(), infer_missing)
AttributeError: 'str' object has no attribute 'keys'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/vagrant/Documents/study/python/bar.py", line 24, in <module>
    school = School.from_dict(d_school)
  File "/home/vagrant/.pyenv/versions/3.10.2/lib/python3.10/site-packages/dataclasses_json/api.py", line 72, in from_dict
    return _decode_dataclass(cls, kvs, infer_missing)
  File "/home/vagrant/.pyenv/versions/3.10.2/lib/python3.10/site-packages/dataclasses_json/core.py", line 201, in _decode_dataclass
    init_kwargs[field.name] = _decode_generic(field_type,
  File "/home/vagrant/.pyenv/versions/3.10.2/lib/python3.10/site-packages/dataclasses_json/core.py", line 265, in _decode_generic
    res = type_(xs)
  File "/home/vagrant/.pyenv/versions/3.10.2/lib/python3.10/typing.py", line 941, in __call__
    raise TypeError(f"Type {self._name} cannot be instantiated; "
TypeError: Type List cannot be instantiated; use list() instead

直背的なエラーはAttributeErrorなのですが、間接的にTypeErrorも発生しました。
これは、dataclasses_json/core.pyのtype_(xs)で、typing.List(...)を実行しているためです。

なお、"Type List cannot be instantiated; use list() instead"のメッセージに従って、peopleの型をtyping.List[Person]からlist[Person]に変更すると、エラーは発生しません。

$ python ~/Documents/study/python/bar.py
School(name='tokyo', people=[])

ただし、peopleの値は空リストになります。これは正しくありません。またエラーが発生しないので、間違っていることにも気付けません。

補足

School.from_dictではなくSchool.schema().loadを実行すれば、型が異なるときにValidationErrorが発生します。

school = School.schema().load(d_school)
# ValidationError: {'people': {0: {'type': ['Not a valid mapping type.']}}}

型を意識したコードを書く場合は、schema().loadを使った方がよさそうです。