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Read typed settings from environment variables

Load configuration from the environment with defaults, type conversion and clear errors for missing values.

Python
import os


def env(name, default=None, cast=str):
    raw = os.environ.get(name)
    if raw is None or raw == "":
        if default is None:
            raise RuntimeError(f"Missing required environment variable {name}")
        return default
    if cast is bool:
        return raw.strip().lower() in {"1", "true", "yes", "on"}
    try:
        return cast(raw)
    except ValueError as exc:
        raise RuntimeError(f"Environment variable {name} must be {cast.__name__}") from exc

Example / expected output

Output
PORT = env("PORT", 8000, int)
DEBUG = env("DEBUG", False, bool)
DATABASE_URL = env("DATABASE_URL")  # required

How it works

Configuration that varies between deployments belongs in environment variables. Converting and validating at startup fails fast with a readable message instead of crashing later. Never log secret values.

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