Include possible enum values in pydantic model

Question

I have a model ModelWithEnum that holds an enum value. In addition to that value, I want the model to output all possible values from that enum (those enums are range-like, e.g. A,B,C; A,B,C,D etc.).

I made EnumModel a GenericModel since I don't want a new model for every Enum class. I am doing my first steps with generics and not sure, whether I am on the right track.

Here's what I want to achieve

# `ModelWithEnum` holds a `enum` field of type `EnumsAC`, # so possible enum values would be "A", "B", "C" model = ModelWithEnum(enum={"value": "A"}) assert model.enum.value == "A" assert model.enum.possible_values == ["A", "B", "C"]

Full sample code:

from enum import Enum from typing import Generic, List, Optional, TypeVar from pydantic.generics import GenericModel from pydantic import BaseModel EnumT = TypeVar("EnumT") class EnumsAC(str, Enum): A = "A" B = "B" C = "C" class EnumsAE(str, Enum): """Another Enums class""" A = "A" B = "B" C = "C" D = "D" E = "E" class EnumModel(GenericModel, Generic[EnumT]): value: EnumT # How can I auto-fill this list with all possible values from EnumT # like if I hardcoded e.g. `list(EnumsAC)` possible_values: List[str] = [] class ModelWithEnum(BaseModel): enum: EnumModel[EnumsAC] # `ModelWithEnum` holds a `enum` field of type `EnumsAC`, # so possible enum values would be "A", "B", "C" model = ModelWithEnum(enum={"value": "A"}) assert model.enum.value == "A" # ok assert model.enum.possible_values == ["A", "B", "C"] # fails

alex_noname · Accepted Answer · 2021-07-06 08:56:36Z

You could use root_validator for autocomplete possible values. Using your model as an example:

class EnumModel(GenericModel, Generic[EnumT]): value: EnumT possible_values: List[str] = [] class Config: validate_assignment = True @root_validator def root_validate(cls, values): values["possible_values"] = [item for item in values['value'].__class__] return values

Beautiful! What difference does validate_assignment make here? I don't quite understand the description from the doc: "whether to perform validation on assignment to attributes (default: False)"
Sets whether the validator will kick in when assigning a new value to fields, and not just when creating an object

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