Compatibility issues when converting stdlib data classes to pydantic data classes

[souloss]

Checks

• I added a descriptive title to this issue
• I have searched (google, github) for similar issues and couldn't find anything
• I have read and followed the docs and still think this is a bug

Bug

Output of python -c "import pydantic.utils; print(pydantic.utils.version_info())":

(.venv) [root@localhost py]# python -c "import pydantic.utils; print(pydantic.utils.version_info())"
             pydantic version: 1.8.2
            pydantic compiled: False
                 install path: /root/py/.venv/lib/python3.10/site-packages/pydantic
               python version: 3.10.1 (main, Dec  9 2021, 08:55:38) [GCC 4.8.5 20150623 (Red Hat 4.8.5-44)]
                     platform: Linux-4.4.0-19041-Microsoft-x86_64-with-glibc2.17
     optional deps. installed: ['dotenv', 'email-validator', 'typing-extensions']
(.venv) [root@localhost  py]# 

from dataclasses import dataclass
from typing import List
from dataclasses import field
import pydantic

@dataclass
class A:
    b: int = 0
    c: List[int] = field(default_factory=list)

pydantic.dataclasses.dataclass(A)
...

output:

(.venv) [root@localhost  py]# python3 test/utils/test_pydanic_bug.py 
Traceback (most recent call last):
  File "/root/py/test/utils/test_pydanic_bug.py", line 15, in <module>
    pydantic.dataclasses.dataclass(A)
  File "/root/py/.venv/lib/python3.10/site-packages/pydantic/dataclasses.py", line 257, in dataclass
    return wrap(_cls)
  File "/root/py/.venv/lib/python3.10/site-packages/pydantic/dataclasses.py", line 252, in wrap
    return _process_class(cls, init, repr, eq, order, unsafe_hash, frozen, config)
  File "/root/py/.venv/lib/python3.10/site-packages/pydantic/dataclasses.py", line 160, in _process_class
    cls: Type['Dataclass'] = dataclasses.dataclass(  # type: ignore
  File "/usr/local/python3.10/lib/python3.10/dataclasses.py", line 1185, in dataclass
    return wrap(cls)
  File "/usr/local/python3.10/lib/python3.10/dataclasses.py", line 1176, in wrap
    return _process_class(cls, init, repr, eq, order, unsafe_hash,
  File "/usr/local/python3.10/lib/python3.10/dataclasses.py", line 1025, in _process_class
    _init_fn(all_init_fields,
  File "/usr/local/python3.10/lib/python3.10/dataclasses.py", line 546, in _init_fn
    raise TypeError(f'non-default argument {f.name!r} '
TypeError: non-default argument 'c' follows default argument

because The stdlib dataclass passes def _process_class(cls, init, repr, eq, order, unsafe_hash, frozen,match_args, kw_only, slots): After processing the ordinary class once, some field class attributes will be deleted, and they will be set to _FIELDS. this process cannot be repeated.

[samuelcolvin]

Would this be fixed by #2557?

[souloss]

It is a pity that I just cloned the code of PrettyWood and the test result failed.

[souloss]

But this seems to be just a small problem, very easy.

[PrettyWood]

Hi @witchc
The code you shared works well with #2557. In which way does it not solve your issue?

[souloss]

@PrettyWood
Maybe there is a problem with my test method?
My test steps are as follows:

[root@localhost ~]# git clone https://github.com/PrettyWood/pydantic.git
Cloning into 'pydantic'...
remote: Enumerating objects: 10878, done.
remote: Counting objects: 100% (217/217), done.
remote: Compressing objects: 100% (119/119), done.
remote: Total 10878 (delta 135), reused 158 (delta 96), pack-reused 10661
Receiving objects: 100% (10878/10878), 4.33 MiB | 2.44 MiB/s, done.
Resolving deltas: 100% (8224/8224), done.
Checking connectivity... done.
[root@localhost ~]# cd pydantic/
[root@localhost pydantic]# python3 -m venv .venv
[root@localhost pydantic]# source .venv/bin/activate
(.venv) [root@localhost pydantic]# pip3 install -r requirements.txt 
Ignoring dataclasses: markers 'python_version < "3.7"' don't match your environment
Looking in indexes: https://pypi.tuna.tsinghua.edu.cn/simple
Collecting Cython==0.29.25 (from -r requirements.txt (line 3))
  Downloading https://pypi.tuna.tsinghua.edu.cn/packages/a6/e0/74dfae7ef24e036538269061aa7d82132c1de84cfb31278927996c09033e/Cython-0.29.25-cp37-cp37m-manylinux_2_5_x86_64.manylinux1_x86_64.whl (2.0MB)
    100% |████████████████████████████████| 2.0MB 705kB/s 
Collecting devtools==0.8.0 (from -r requirements.txt (line 4))
  Downloading https://pypi.tuna.tsinghua.edu.cn/packages/54/11/32e995d0978b8898fbdb35179186b0155355db2fdd20f7058761b27006e2/devtools-0.8.0-py3-none-any.whl
Collecting email-validator==1.1.3 (from -r requirements.txt (line 5))
  Using cached https://pypi.tuna.tsinghua.edu.cn/packages/9e/e4/e01e92092fdac940f10fa4c8ac3481bf70fc74023a76f5c72020c9445e68/email_validator-1.1.3-py2.py3-none-any.whl
Collecting typing-extensions==4.0.1 (from -r requirements.txt (line 7))
  Using cached https://pypi.tuna.tsinghua.edu.cn/packages/05/e4/baf0031e39cf545f0c9edd5b1a2ea12609b7fcba2d58e118b11753d68cf0/typing_extensions-4.0.1-py3-none-any.whl
Collecting python-dotenv==0.19.2 (from -r requirements.txt (line 8))
  Using cached https://pypi.tuna.tsinghua.edu.cn/packages/0e/f1/0317f4b2c5284075a2154fe95539b43c0acecbcb86fe80fcb2645803edd9/python_dotenv-0.19.2-py2.py3-none-any.whl
Collecting executing<1.0.0,>=0.8.0 (from devtools==0.8.0->-r requirements.txt (line 4))
  Downloading https://pypi.tuna.tsinghua.edu.cn/packages/ba/64/59e024b685666514cb20ffc2463a8b062df8e6c36efc5199cb422b728b78/executing-0.8.2-py2.py3-none-any.whl
Collecting asttokens<3.0.0,>=2.0.0 (from devtools==0.8.0->-r requirements.txt (line 4))
  Downloading https://pypi.tuna.tsinghua.edu.cn/packages/16/d5/b0ad240c22bba2f4591693b0ca43aae94fbd77fb1e2b107d54fff1462b6f/asttokens-2.0.5-py2.py3-none-any.whl
Collecting dnspython>=1.15.0 (from email-validator==1.1.3->-r requirements.txt (line 5))
  Downloading https://pypi.tuna.tsinghua.edu.cn/packages/f5/2d/ae9e172b4e5e72fa4b3cfc2517f38b602cc9ba31355f9669c502b4e9c458/dnspython-2.1.0-py3-none-any.whl (241kB)
    100% |████████████████████████████████| 245kB 354kB/s 
Collecting idna>=2.0.0 (from email-validator==1.1.3->-r requirements.txt (line 5))
  Using cached https://pypi.tuna.tsinghua.edu.cn/packages/04/a2/d918dcd22354d8958fe113e1a3630137e0fc8b44859ade3063982eacd2a4/idna-3.3-py3-none-any.whl
Collecting six (from asttokens<3.0.0,>=2.0.0->devtools==0.8.0->-r requirements.txt (line 4))
  Using cached https://pypi.tuna.tsinghua.edu.cn/packages/d9/5a/e7c31adbe875f2abbb91bd84cf2dc52d792b5a01506781dbcf25c91daf11/six-1.16.0-py2.py3-none-any.whl
Installing collected packages: Cython, executing, six, asttokens, devtools, dnspython, idna, email-validator, typing-extensions, python-dotenv
Successfully installed Cython-0.29.25 asttokens-2.0.5 devtools-0.8.0 dnspython-2.1.0 email-validator-1.1.3 executing-0.8.2 idna-3.3 python-dotenv-0.19.2 six-1.16.0 typing-extensions-4.0.1
You are using pip version 19.0.3, however version 21.3.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
(.venv) [root@localhost pydantic]# cat <<EOF > tests/
check_tag.py                       test_abc.py                        test_color.py                      test_edge_cases.py                 test_json.py                       test_parse.py                      test_types.py
conftest.py                        test_aliases.py                    test_construction.py               test_errors.py                     test_main.py                       test_private_attributes.py         test_typing.py
__init__.py                        test_annotated.py                  test_create_model.py               test_fastapi.sh                    test_model_signature.py            test_schema.py                     test_utils.py
mypy/                              test_annotated_types.py            test_dataclasses.py                test_forward_ref.py                test_networks_ipaddress.py         test_settings.py                   test_validators_dataclass.py
requirements-linting.txt           test_assert_in_validators.py       test_datetime_parse.py             test_generics.py                   test_networks.py                   test_tools.py                      test_validators.py
requirements-testing.txt           test_callable.py                   test_decorator.py                  test_hypothesis_plugin.py          test_orm_mode.py                   test_types_payment_card_number.py  test_version.py
(.venv) [root@localhost pydantic]# cat <<EOF > tests/test_dataclass.py
> from dataclasses import dataclass
> from typing import List
> from dataclasses import field
> import pydantic
> 
> @dataclass
> class A:
>     b: int = 0
>     c: List[int] = field(default_factory=list)
> 
> pydantic.dataclasses.dataclass(A)
> EOF
(.venv) [root@localhost pydantic]# export PYTHONPATH=$(pwd)
(.venv) [root@localhost pydantic]# python3 tests/test_dataclass.py 
Traceback (most recent call last):
  File "tests/test_dataclass.py", line 11, in <module>
    pydantic.dataclasses.dataclass(A)
  File "/root/pydantic/pydantic/dataclasses.py", line 256, in dataclass
    return wrap(_cls)
  File "/root/pydantic/pydantic/dataclasses.py", line 251, in wrap
    return _process_class(cls, init, repr, eq, order, unsafe_hash, frozen, config)
  File "/root/pydantic/pydantic/dataclasses.py", line 160, in _process_class
    _cls, init=init, repr=repr, eq=eq, order=order, unsafe_hash=unsafe_hash, frozen=frozen
  File "/usr/local/python3/lib/python3.7/dataclasses.py", line 991, in dataclass
    return wrap(_cls)
  File "/usr/local/python3/lib/python3.7/dataclasses.py", line 983, in wrap
    return _process_class(cls, init, repr, eq, order, unsafe_hash, frozen)
  File "/usr/local/python3/lib/python3.7/dataclasses.py", line 904, in _process_class
    else 'self',
  File "/usr/local/python3/lib/python3.7/dataclasses.py", line 490, in _init_fn
    raise TypeError(f'non-default argument {f.name!r} '
TypeError: non-default argument 'c' follows default argument
(.venv) [root@localhost pydantic]# 

[souloss]

@PrettyWood
Sorry, I made a low-level mistake and didn't switch branches.

[souloss]

@PrettyWood
It does work well with the code on the correct branch, great.
I will close this issue.