Example of handling application config using pydantic https://github.com/samuelcolvin/pydantic

config_with_pydantic.py

# Example of handling application config using pydantic https://github.com/samuelcolvin/pydantic
# Use python>=3.6 and install pydantic==1.3.1 to run it

import unittest
from dataclasses import FrozenInstanceError
from typing import Optional

from pydantic.dataclasses import dataclass
from pydantic import ValidationError

# With `frozen=True` we ensure immutability of data
@dataclass(frozen=True)
class Location:
    # Writing types allows us to validate data, also if provided value
    # is e.g. int - pydantic tries to cast it to string. If fails - ValidationError is raised
    street: str
    house_number: int
    city: str
    postal_code: str
    flat_number: Optional[int] = None


@dataclass(frozen=True)
class User:
    first_name: str
    last_name: str
    location: Location


good_cfg_1 = {
    "first_name": "John",
    "last_name": "Snow",
    "location": {
        "street": "Frozen St.",
        "house_number": 17,
        "city": "Winterfell",
        "postal_code": "34-567",
    },
}

john_snow_1: User = User(**good_cfg_1)

assert john_snow_1.location.postal_code == good_cfg_1["location"]["postal_code"]
assert john_snow_1.location.flat_number is None

good_cfg_2 = {
    "first_name": "John",
    "last_name": "Snow",
    "location": {
        "street": "Frozen St.",
        "house_number": 17,
        "city": "Winterfell",
        "flat_number": 15,
        "postal_code": 12123,
    },
}

john_snow_2 = User(**good_cfg_2)

assert john_snow_2.location.postal_code == str(good_cfg_2["location"]["postal_code"])
assert john_snow_2.location.flat_number == good_cfg_2["location"]["flat_number"]


with unittest.TestCase().assertRaises(FrozenInstanceError):
    john_snow_2.last_name = "Targaryen"

with unittest.TestCase().assertRaises(FrozenInstanceError):
    john_snow_2.location.flat_number = 16

with unittest.TestCase().assertRaises(ValidationError):
    bad_cfg = {**good_cfg_2, **{"location": {"flat_number": "abc"}}}
    john_snow_2 = User(**bad_cfg)