literal_pydantic_example.py

from typing import Literal, List
from pydantic import BaseModel, Field


class User(BaseModel):
    name: str
    roles: List[Literal["Registered", "Moderator", "Admin"]] = Field(
        default_factory=list
    )


jon_doe = User.parse_obj({"name": "Jon Doe", "roles": []})
jon_skeet = User.parse_obj({"name": "Jon Skeet", "roles": ["Registered", "Admin"]})
print(jon_skeet.dict())

# This fails - as expected!
# unexpected value; permitted: 'Registered', 'Moderator', 'Admin'
# (type=value_error.const;
#  given=foo;
#  permitted=('Registered', 'Moderator', 'Admin')
# )
User.parse_obj({"name": "Jon Doe", "roles": ["foo"]})