override field alias from subclass in Pydantic

I have 2 models, 1 subclassing the other:

from pydantic import BaseModel
from typing import List

class Model1(BaseModel):
    names: List[str]

class Model2(Model1):
    # define here an alias for names -> e.g. "firstnames"
    pass

data = { "names": ["rodrigo", "julien", "matthew", "bob"] }
# Model1(**data).dict()  -> gives {'names': ['rodrigo', 'julien', 'matthew', 'bob']}
# Model2(**data).dict()  -> gives {'firstnames':  ['rodrigo', 'julien', 'matthew', 'bob']}

How can I accomplish this ?

Answer

You don’t need to subclass to accomplish what you want (unless your need is more complex than your example).

For import: Add the Config option to allow_population_by_field_name so you can add the data with names or firstnames

For export: Add by_alias=True to the dict() method to control the output

from pydantic import BaseModel
from typing import List


class Model(BaseModel):
    names: List[str] = Field(alias="firstnames")

    class Config:
        allow_population_by_field_name = True


def main():
    data = {"names": ["rodrigo", "julien", "matthew", "bob"]}
    model = Model(**data)
    print(model.dict())
    print(model.dict(by_alias=True))


if __name__ == '__main__':
    main()

yields:

{'names': ['rodrigo', 'julien', 'matthew', 'bob']}
{'firstnames': ['rodrigo', 'julien', 'matthew', 'bob']}