Can I get incoming extra fields from Pydantic?

Question

I have defined a pydantic Schema with extra = Extra.allow in Pydantic Config.

Is it possible to get a list or set of extra fields passed to the Schema separately.

For ex:

from pydantic import BaseModel as pydanticBaseModel
class BaseModel(pydanticBaseModel):
    name: str

    class Config:
        allow_population_by_field_name = True
        extra = Extra.allow

I pass below JSON:

   {
    "name": "Name",
    "address": "bla bla",
    "post": "post"
   }

I need a function from pydantic, if available which will return all extra fields passed. like: {"address", "post"}

Answer 1

As far as I know, there is no out-of-the-box solution for this. But since you have access to all "raw" passed data, including extra fields, in the pre root validator, you can put them there in a separate dictionary.

An example is taken from here. Thanks to @PrettyWood for providing it:

from typing import Any, Dict, Optional

from pydantic import BaseModel, Field, root_validator


class ComposeProject(BaseModel):
    versio: Optional[str] = Field(alias='version')  # just to show that it supports alias too
    extra: Dict[str, Any]

    @root_validator(pre=True)
    def build_extra(cls, values: Dict[str, Any]) -> Dict[str, Any]:
        all_required_field_names = {field.alias for field in cls.__fields__.values() if field.alias != 'extra'}  # to support alias

        extra: Dict[str, Any] = {}
        for field_name in list(values):
            if field_name not in all_required_field_names:
                extra[field_name] = values.pop(field_name)
        values['extra'] = extra
        return values


project = ComposeProject(**{
  "version": "3",
  "services": ...
})
print(project.version)  # => '3'
print(project.extra)  # => {'services': Ellipsis}