default=[] and default_factory=list marks field as Optional in OpenAPI documentation

[JonasKs]

Hi,

When I have a model like this:

class X(BaseModel):
    list_item: list[str] = Field(default=[])

The list will always be there, it won't be None. I have also not type annotated it as list[str] | None. However, the OpenAPI documentation does not mark it as required.

The solution is to do this:

class X(BaseModel):
    list_item: list[str] = Field(default=...)

but that also forces me to always create X(list_item=[]) instead of just X(). Not the end of the world, but for some large models this is a bit annoying.

Is OpenAPI documentation generated without using type hints, since this don't work?
Any clean workarounds?

[JonasKs]

I guess a decent workaround is to do this:

class X(BaseModel):
    list_item: list[str] = Field(default=[])

    class Config:
        schema_extra = {
           'required': ['list_item']
        }

Even though the behavior seems a bit counterintuitive to me.

[samuelcolvin]

Moved to issue and replied there, see #4697.