Pydantic dataclasses do not respect the extra-fields in Config

Question

Pydantic dataclasses do not seem to respect the configuration passed in the @dataclass-decorator. I am wondering if this is a bug or expected functionality? The documentation indicates that the Config is respected.

pydantic.dataclasses.dataclass’s arguments are the same as the standard decorator, except one extra keyword argument config which has the same meaning as Config.

In particular I would like to ignore extra fields when initialising the object. The documentation suggests that the default behaviour is Extra.ignore, but it does not seem to work. Making this explicit does not seem to have an effect either…

from pydantic.dataclasses import dataclass
>>> class C:
...     extra = Extra.ignore
...
>>> @dataclass(config=C)
... class Foo:
...     a: str
...     b: str
...
>>> Foo(**{"a": "bar", "b": "foo", "c": 1})
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: __init__() got an unexpected keyword argument 'c'

Please complete:

• OS: os x
• Python version:

>>> import sys; print(sys.version)
3.7.2 (default, Mar 22 2019, 11:08:57)
[Clang 10.0.0 (clang-1000.10.44.4)]

• Pydantic version:

>>> import pydantic; print(pydantic.VERSION)
1.0

[ilya-kolpakov]

To me this sounds unnecessarily complicated. If you want extra, best to use BaseModel.

At the very least the docs should mention that the extra setting is ignored on dataclasses. EDIT: It’s a massive turn-off for using pydantic dataclasses in the context of FastApi

[PrettyWood]

I guess we could do something like this