Use typing.Literal in dataclass reader

Question

I have a csv file that I'd like to process to a dataclass. I'd like to check that the grades in my dataset are only from a prespecified list, if this is not the case I'd like to log an error/warning. My class looks as follows

from dataclasses import dataclass
from typing import Literal

grade_options = Literal['1A', '1B', '1C']

class Student:
    name: str
    age: int
    grade: grade_options

I read my csv file (using the dataclass-csv library), yet it has problems to instantiate this type

from dataclass_csv import DataclassReader

with open('students.csv', encoding="utf-8-sig") as read_csv:
    reader = DataclassReader(read_csv, Student, delimiter=";")
    students = [student for student in reader]

This will result in a TypeError: Cannot instantiate typing.Literal

Is there any other option than creating a manual checker to see if my values in the csv file are one of the specified options?

Answer 1

I just ran into this myself. You have to use concrete classes that extend Enum.

Based on "Create an enum class" in the tutorial:

from enum import Enum


class Grade(str, Enum):
    _1a: '1A'
    _1b: '1B'
    _1c: '1C'

class Student:
    name: str
    age: int
    grade: Grade