Pydantic "Not Recognizing" Field in BaseModel with Default Value of Type

[ntenenz]

Checks

• [X ] I added a descriptive title to this issue
• [X ] I have searched (google, github) for similar issues and couldn't find anything
• [X ] 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())":

pydantic version: 1.7.3
pydantic compiled: True
python version: 3.8.2 (default, Mar 13 2020, 10:14:16)  [GCC 9.3.0]
platform: Linux-4.19.128-microsoft-standard-x86_64-with-glibc2.29
optional deps. installed: ['typing-extensions']

import pydantic
from typing import Type, Sequence, Union

class T:
    pass

class Model(pydantic.BaseModel):
    t: Union[Type[T], Sequence[Type[T]]] = T
    
    @pydantic.validator("t", always=True)
    def make_tuple(cls, v):
        if isinstance(v, Sequence):
            return tuple(v)
        return v,

# ConfigError: Validators defined with incorrect fields: make_tuple (use check_fields=False if you're inheriting from the model and intended this)

Note: If the field is marked optional and the default value is set to None, the code works without issue.

import pydantic
from typing import Type, Sequence, Union, Optional

class T:
    pass

class Model(pydantic.BaseModel):
    t: Optional[Union[Type[T], Sequence[Type[T]]]] = None
    
    @pydantic.validator("t", always=True)
    def make_tuple(cls, v):
        if not v:
            return T,
        elif isinstance(v, Sequence):
            return tuple(v)
        return v,

Model()
# Model(t=(<class '__main__.T'>,))

Perhaps I am missing something obvious in my sleep-deprived stupor?

[PrettyWood]

Hello @ntenenz and thanks for reporting!
It looks like a bug. It seems like the default value with this type is not taken into account in the metaclass causing Model.__fields__ to not have the t key, which causes this error.
In the meantime you can use Field to force it: t: Union[Type[T], Sequence[Type[T]]] = Field(T)

EDIT: opened a PR with the fix :)

Happy holiday season 🎅

[ntenenz]

Thanks for the prompt response and fix @PrettyWood. Happy holidays! ❄️❄️❄️