Getting Started

Installation

pip install molcrafts-molcfg

The PyPI distribution name is molcrafts-molcfg; the import name is molcfg.

For local development:

pip install -e ".[dev]"
pip install -e ".[docs]"

First Config

from molcfg import Config

cfg = Config({"app": {"name": "demo", "debug": False}})

# attribute access
assert cfg.app.name == "demo"

# dotted-path access
assert cfg["app.name"] == "demo"

# containment check
assert "app.debug" in cfg

Mutating a Config

cfg.app.name = "updated"
cfg["app.debug"] = True

Nested dicts are automatically wrapped into child Config objects.

Freezing and rollback

cfg.freeze()
# cfg.app.name = "x"  # raises FrozenConfigError

cfg.unfreeze()
cfg.snapshot()
cfg.app.name = "temporary"
cfg.rollback()
assert cfg.app.name == "updated"

Layered loading

Later sources win using DEEP_MERGE by default:

from molcfg import CliSource, ConfigLoader, DictSource, EnvSource

cfg = ConfigLoader([
    DictSource({"db": {"host": "localhost", "port": 5432}}, name="defaults"),
    EnvSource(prefix="APP", name="env"),
    CliSource(["--db.port=6432"], name="cli"),
]).load()

assert cfg["db.port"] == 6432

Source tracking

info = cfg.meta("db.port")
# {"source": "cli", "history": ("defaults", "cli")}

source is the last writer. history lists every source that touched the key, in order.

Serialization

d = cfg.to_dict()
s = cfg.to_json()
s = cfg.to_json(indent=2)

Change callbacks

def on_change(path: str, new_value, old_value) -> None:
    print(f"{path}: {old_value!r} -> {new_value!r}")

cfg.on_change(on_change)
cfg.app.name = "watched"
# app.name: 'demo' -> 'watched'