saneconfig

Dead-simple typed config loader for dataclasses:

• defaults
• TOML file(s)
• environment variables

with great errors and provenance ("where did this value come from?").

Python 3.11+.

Core package has zero runtime dependencies; optional extras:

• saneconfig[dotenv] for .env file support.

Install

pip install saneconfig
# optional .env support
pip install "saneconfig[dotenv]"

Quick start

from dataclasses import dataclass
from saneconfig import load, REQUIRED


@dataclass
class AppConfig:
    debug: bool = False
    port: int = 8080
    database_url: str = REQUIRED


cfg = load(
    AppConfig,
    env_prefix="APP",
    files=["config.toml", "config.local.toml"],
)

print(cfg.port)

Precedence (highest wins)

1. CLI args (argv=True or argv=[...])
2. Environment variables
3. .env file values (when dotenv is enabled)
4. TOML files (later overrides earlier)
5. Dataclass defaults

TOML example

debug = true
port = 9000
database_url = "postgresql://user:pass@localhost:5432/mydb"

Nested dataclasses map to TOML tables:

[db]
host = "localhost"
port = 5432

Env var mapping

With env_prefix="APP":

• APP_PORT=9000 -> port
• APP_DEBUG=true -> debug
• nested via __: APP_DB__HOST=localhost -> db.host

Booleans accept: true/false, yes/no, on/off, 1/0 (case-insensitive).

Lists in env vars use JSON:

APP_ALLOWED='["a","b"]'

CLI overrides

Enable CLI parsing by passing argv=True (uses sys.argv[1:]) or provide a list explicitly:

cfg = load(
    AppConfig,
    env_prefix="APP",
    argv=["--port=9001", "--db.host=db.internal"],
)

Supported form: --key=value with dotted nesting (--db.host=x).

Provenance / debugging

cfg, report = load(
    AppConfig,
    env_prefix="APP",
    files=["config.toml", "config.local.toml"],
    return_report=True,
)

print(report)

Example output:

database_url='postgresql://...' (env:APP_DATABASE_URL)
debug=False (default)
port=9000 (file:config.toml)

Schema docs

You can include richer docs using dataclass metadata:

from dataclasses import dataclass, field

@dataclass
class AppConfig:
    port: int = field(default=8080, metadata={"help": "HTTP listen port"})

from saneconfig import dump_schema
print(dump_schema(AppConfig, env_prefix="APP"))

dump_schema(...) includes a Help column using field(metadata={"help": ...}).

Errors that help

If a value cannot be converted:

ConfigError: port expected int but got "eighty"
  source: env:APP_PORT
  hint: Use a valid int value.

If required values are missing:

ConfigError: missing required configuration values:
  - database_url

Supported types (v0.1)

• str, int, float, bool
• Optional[T]
• list[T] (TOML arrays or JSON arrays in env)
• Literal[...]
• nested dataclasses
• pathlib.Path
• dict[str, T] (TOML table or JSON object in env)

Non-goals (by design)

• profiles/composition systems
• interpolation DSLs
• frameworks and global state

MIT Licensed.

---

A tiny example you can run

from dataclasses import dataclass
from typing import Literal, Optional

from saneconfig import REQUIRED, load


@dataclass
class DB:
    host: str = "localhost"
    port: int = 5432


@dataclass
class App:
    mode: Literal["dev", "prod"] = "dev"
    debug: bool = False
    port: int = 8080
    api_key: str = REQUIRED
    db: DB = DB()
    notes: Optional[str] = None


cfg, report = load(App, env_prefix="APP", files=["config.toml"], return_report=True)
print(cfg)
print(report)