Pydantic v2

You can use the extra field in the model_config class attribute to forbid extra attributes during model initialisation (by default, additional attributes will be ignored).

For example:

from pydantic import BaseModel, ConfigDict

class Pet(BaseModel):
    model_config = ConfigDict(extra="forbid")

    name: str

data = {
    "name": "some name",
    "some_extra_field": "some value",
}

my_pet = Pet.model_validate(data)   # <- effectively the same as Pet(**pet_data)

will raise a ValidationError:

ValidationError: 1 validation error for Pet
some_extra_field
  Extra inputs are not permitted [type=extra_forbidden, input_value='some value', input_type=str]
    For further information visit https://errors.pydantic.dev/2.7/v/extra_forbidden

Works as well when the model is "nested", e.g.:

class PetModel(BaseModel):
    my_pet: Pet
    n: int

pet_data = {
    "my_pet": {"name": "Some Name", "invalid_field": "some value"},
    "n": 5,
}

pet_model = PetModel.model_validate(pet_data)
# Effectively the same as
# pet_model = PetModel(my_pet={"name": "Some Name", "invalid_field": "some value"}, n=5)

will raise:

ValidationError: 1 validation error for PetModel
my_pet.invalid_field
  Extra inputs are not permitted [type=extra_forbidden, input_value='some value', input_type=str]
    For further information visit https://errors.pydantic.dev/2.7/v/extra_forbidden

NB: As you can see, extra has the type ExtraValues now, and its value will get validated by ConfigDict. This means it's not possible to accidentally provide an unsupported value for extra (e.g. having a typo), i.e. something like ConfigDict(extra="fordib") will fail with a SchemaError.

Pydantic v1

You can use the extra field in the Config class to forbid extra attributes during model initialisation (by default, additional attributes will be ignored).

For example:

from pydantic import BaseModel, Extra

class Pet(BaseModel):
    name: str

    class Config:
        extra = Extra.forbid

data = {
    "name": "some name",
    "some_extra_field": "some value",
}

my_pet = Pet.parse_obj(data)   # <- effectively the same as Pet(**pet_data)

will raise a VaidationError:

ValidationError: 1 validation error for Pet
some_extra_field
  extra fields not permitted (type=value_error.extra)

Works as well when the model is "nested", e.g.:

class PetModel(BaseModel):
    my_pet: Pet
    n: int

pet_data = {
    "my_pet": {"name": "Some Name", "invalid_field": "some value"},
    "n": 5,
}

pet_model = PetModel.parse_obj(pet_data)
# Effectively the same as
# pet_model = PetModel(my_pet={"name": "Some Name", "invalid_field": "some value"}, n=5)

will raise:

ValidationError: 1 validation error for PetModel
my_pet -> invalid_field
  extra fields not permitted (type=value_error.extra)

The underscore in from the "id" makes it a class attribute and excludes it from the model. Pydantic info here

You can work around this by calling the attribute "id" and use an alias with an underscore

from pydantic import Field

class UserAPI(BaseSchema, UserBase):
    id: ObjectId = Field(None, alias="_id", title="Primary key", description="mongodb's Primary key")

inspiration from this

Pydantic extra fields behaviour was updated in their 2.0 release. Per their docs, you now don't need to do anything but set the model_config extra field to allow and then can use the model_extra field or __pydantic_extra__ instance attribute to get a dict of extra fields.

from pydantic import BaseModel, Field, ConfigDict


class Model(BaseModel):
    python_name: str = Field(alias="name")

    model_config = ConfigDict(
        extra='allow',
    )

m = Model(**{"name": "Name", "address": "bla bla", "post": "post"}).model_extra
assert m == {'address': 'bla bla', 'post': 'post'}

m = Model(**{"name": "Name", "foobar": "fizz"}).__pydantic_extra__
assert m == {'foobar': 'fizz'}

m = Model(**{"name": "Name"}).__pydantic_extra__
assert m == {}