A quick first pass at a "configurable configuration validator"

config_validate.py

import typing as t
from functools import partial
from inspect import getsource


class ConfigError(ValueError):
    ...


def get_func_name(func: t.Callable) -> str:
    name = func.__name__
    if name == "<lambda>":
        name = getsource(func).split("=")[0].strip()
    return name


def is_type(type: t.Type, key: str, config: dict) -> None:

    if not isinstance((value := config[key]), type):
        raise ConfigError(
            f"{key} must be an instance of {type.__name__}. Was {type(value)}"
        )


is_string = partial(is_type, str)
is_int = partial(is_type, int)


def exactly_n(n: int, keys: list, config: dict) -> None:
    if (actual_n := len((filtered := [i for i in keys if i in config]))) != n:
        raise ConfigError(
            f"Config must contain exactly {n} items from {keys}. Found {actual_n}: {filtered}"
        )


exactly_one = partial(exactly_n, n=1)


def disallowed_keys(keys: list, config: dict) -> bool:
    if present := [k for k in keys if k in config]:
        raise ConfigError(
            f"The following dissalowed keys were found in config: {present}"
        )


def required_keys(keys: list, config: dict) -> bool:
    if not_present := [k for k in keys if k not in config]:
        raise ConfigError(
            f"The following required keys were not found in config: {not_present}"
        )


def pass_filter(filter: t.Callable, key: str, config: dict) -> None:
    if not filter(config[key]):
        raise ConfigError(
            f"The value of config item {key} does not pass {get_func_name(filter)}. Got value: '{config[key]}'"
        )


def validate(validation_rules: dict, config: dict) -> None:
    exceptions = list()

    for key, rule_list in validation_rules.get("value_rules", {}).items():
        for rule in list(rule_list):
            try:
                rule(key=key, config=config)
            except ConfigError as e:
                exceptions.append(e)

    for cr in validation_rules.get("config_rules", []):
        try:
            cr(config=config)
        except ConfigError as e:
            exceptions.append(e)

    print(exceptions)
    e = exceptions.pop(0)
    raise e


if __name__ == "__main__":

    config = {
        "setting1": 1,
        "setting2": None,
        "setting3": " ",
        "color_hex": "#1f42a5",
        "color_code": (165, 42, 42),
    }

    def not_red(value: str) -> bool:
        return value != "red"

    is_truthy = lambda x: x is True

    validation_rules = {
        "value_rules": {
            "setting1": [is_int],
            "setting3": [
                is_string,
                partial(pass_filter, not_red),
                partial(pass_filter, is_truthy),
            ],
        },
        "config_rules": [
            partial(disallowed_keys, keys=["thebadkey", "anotherbadkey"]),
            partial(exactly_one, keys=["color_hex", "color_code"]),
        ],
    }

    validate(validation_rules, config)