liteconf 0.1.0

FeatherConf: lightweight layered configuration loader with environment-aware overrides.

Simpleconf

simpleconf is a lightweight configuration loader focused on deterministic override rules, explicit layering, and ergonomic access patterns. It embraces boring tooling (plain YAML/JSON/TOML) while solving the painful parts typical projects hit:

• predictable ordering across base/, local/, environment, and runtime overrides
• structure-preserving deep merge (lists replace, dicts merge)
• attribute and dict access via a single ConfigView
• environment interpolation with type coercion
• opt-in validation hooks without mandating a heavyweight framework

Why another config loader?

Existing Python options shine in specific niches but often trade simplicity for power:

• dynaconf, hydra, omegaconf ship large abstraction layers, CLIs, or plugin registries
• pydantic-settings and environs center on .env files and type validation, not layered YAML
• configparser and ConfigObj struggle with nested structures

simpleconf keeps the learning curve flat while covering the 90% case of layered application configs.

Install

pip install liteconf

Quick Start (Practical)

Consider this minimal layout (two folders + one JSON):

conf/
  base/
    service.yml
  local/
    service.yml
extra.json

conf/base/service.yml

service:
  url: https://api.base
  retries: 2
  features:
    cache: false
    logging: warn   # defined only in base

conf/local/service.yml

service:
  url: https://api.local          # overrides base
  retries: 3                      # overrides base; later overridden by extra.json
  features:
    cache: true                   # overrides base
    tracing: true                 # added by local
  webhook: "${SERVICE_WEBHOOK:https://hooks.local/notify}"  # env placeholder with default

extra.json

{
  "service": {
    "retries": 5,                 
    "timeout": 10,                
    "endpoint": { "health": "/health" }  
  }
}

Load everything with explicit source order (later wins):

from pathlib import Path
from simpleconf import ConfigManager, DirectorySource, FileSource, EnvSource

manager = ConfigManager([
    DirectorySource(Path("conf/base"), optional=False),
    DirectorySource(Path("conf/local"), optional=True),
    FileSource(Path("extra.json"), optional=True),
    # Optional: environment overlay, e.g. APP__SERVICE__TIMEOUT=30
    EnvSource(prefix="APP", delimiter="__", infer_types=True),
])

cfg = manager.load()

# Value defined only in base
assert cfg.get("service.features.logging") == "warn"

# Values overridden by local
assert cfg.service.url == "https://api.local"
assert cfg.service.features.cache is True

# Value added by local
assert cfg.get("service.features.tracing") is True

# Overridden by local, then by extra.json (final)
assert cfg.service.retries == 5  # base=2 -> local=3 -> extra.json=5

# Values provided only by extra.json
assert cfg.service.timeout == 10
assert cfg.service.endpoint.health == "/health"

# You can use attribute-style or dotted lookups interchangeably
assert cfg.service.url == cfg.get("service.url")

# Save a copy if useful for debugging
cfg.save("debug_config.yml")

Notes:

• The filename forms the first key: service.yml becomes top-level key service.
• Attribute access (cfg.service.url) and dotted lookups (cfg.get("service.url")) both work.
• Source order matters: items from later sources override earlier ones.

Features

• deterministic source ordering; later sources override earlier ones
• automatic parsing for .yml/.yaml, .json, and .toml
• ${ENV_VAR:default} interpolation inside string values
• environment overlays with case-insensitive prefix matching
• ConfigView offering .get() with dotted paths, .to_dict(), .as_dataclass()
• stateless loader: creating a new manager or calling reload() rereads from disk

Environment Overrides (Two Ways)

1. Inline placeholders inside files (resolved at load time):

# in conf/local/service.yml
service:
  webhook: "${SERVICE_WEBHOOK:https://hooks.local/notify}"

• If SERVICE_WEBHOOK is set in the environment, its value is used.
• Otherwise, the default https://hooks.local/notify is used.

2. Environment overlay with a prefix (no file edits needed):

# Let’s suppose you want to raise the timeout via an env var
export APP__SERVICE__TIMEOUT=30
pytest  # or run your app; the manager will pick it up

With EnvSource(prefix="APP", delimiter="__", infer_types=True), keys map as:

• APP__SERVICE__TIMEOUT=30 -> service.timeout = 30 (int)
• APP__SERVICE__FEATURES__CACHE=false -> service.features.cache = False (bool)

Loading: One-Call vs Explicit Sources

• Quick one-call loader for folders only:

  from simpleconf import load
  cfg = load(layers=[Path("conf/base"), Path("conf/local")])
  # Recursively loads .yml/.yaml/.json/.toml; later folders override earlier
  

• Explicit sources for full control (files, env, dict overlays, optional flags):

  from simpleconf import ConfigManager, DirectorySource, FileSource, EnvSource, DictOverlay
  manager = ConfigManager([
      DirectorySource(Path("conf/base")),
      DirectorySource(Path("conf/local")),
      FileSource(Path("extra.json")),
      EnvSource(prefix="APP"),
      DictOverlay({"runtime": {"feature_flag": True}}),
  ])
  cfg = manager.load()
  

Use load(...) when you just need layered folders; use ConfigManager when you want to precisely choose and order different kinds of sources.

File Precedence and Duplicate Stems

• Across sources: later sources override earlier ones.
• Within a single folder: files are applied in lexicographic filename order.
• If both messaging.json and messaging.yml exist in the same folder:
  • One-call load(...) (LayeredConfigLoader): both are merged; later filename wins for overlapping keys (usually YAML after JSON).
  • Explicit DirectorySource (ConfigManager): later filename replaces the earlier file’s subtree at that key entirely.

Recommendation: avoid keeping two files with the same stem (e.g., messaging.*) in the same folder. Prefer a single file per logical key per layer to keep intent crystal clear.

Project layout

simpleconf/
|-- pyproject.toml
|-- README.md
|-- src/
|   \-- simpleconf/
|       |-- __init__.py
|       |-- core.py
|       |-- errors.py
|       |-- exceptions.py
|       |-- loader.py
|       |-- manager.py
|       |-- merger.py
|       |-- namespaces.py
|       \-- sources.py
\-- tests/
    |-- conftest.py
    |-- fixtures/
    |   |-- base/
    |   |   \-- messaging.yml
    |   |-- local/
    |   |   \-- messaging.yml
    |   \-- prod/
    |       |-- messaging.json
    |       \-- messaging.yml
    |-- test_loader.py
    \-- test_manager.py

License

MIT — do anything you want, just keep the notice.