config-manager

A lightweight, zero-dependency config loader for Python data-processing pipelines.

• Walks parent directories automatically to find config.json, config.yaml, or config.toml
• Loads .env from the same directory into os.environ (without overwriting existing vars)
• Auto-detects the calling script's name as the active section — no boilerplate
• Special _globals section — its values are merged into every section automatically
• Resolves {{section.key.subkey}} cross-references at arbitrary depth
• Interpolates ${ENV_VAR} placeholders from os.environ in string values
• Attribute-style access with IDE tab-completion (cfg.lr, cfg.paths.raw)
• Clear error messages when a reference can't be resolved

Install

pip install refconf-manager

With YAML support:

pip install "refconf-manager[yaml]"

Quick start

project/
├── config/
│   ├── config.json
│   └── .env
├── preprocess.py
└── pipeline/
    └── train.py   ← ConfigManager() walks up and finds config/config.json

config/config.json

{
    "_globals": {
        "root":    "data/",
        "version": "v2"
    },
    "preprocess": {
        "output": "{{root}}clean.csv"
    },
    "train": {
        "input":   "{{preprocess.output}}",
        "lr":      0.01,
        "run_id":  "{{version}}"
    }
}

train.py

from refconf_manager import ConfigManager

cfg = ConfigManager()       # section="train" detected from filename

cfg["input"]                # → "data/clean.csv"  (resolved via preprocess)
cfg.input                   # → "data/clean.csv"  (attribute-style shorthand)
cfg["lr"]                   # → 0.01
cfg.lr                      # → 0.01
cfg["version"]              # → "v2"  (injected from _globals)
cfg["run_id"]               # → "v2"
cfg.get("device", "cpu")    # → "cpu"  (default)

Use cases

1 — Multi-step pipeline

Each script reads only its own section. {{section.key}} wires outputs to inputs.

# preprocess.py
cfg = ConfigManager()
df.to_csv(cfg["output"])   # saves to "data/clean.csv"

# train.py
cfg = ConfigManager()
df = pd.read_csv(cfg["input"])   # reads "data/clean.csv" automatically

2 — Shared constants with _globals

Put anything shared (paths, versions, DB hosts) in _globals and access it directly in every section without any {{...}} syntax.

{
    "_globals": {
        "db_host": "localhost",
        "root":    "data/"
    },
    "etl":  { "source": "{{root}}raw.csv" },
    "api":  { "host":   "{{db_host}}" }
}

cfg = ConfigManager()
cfg["db_host"]   # available in every section

3 — Deep nested references

Reference values at any depth using dot notation.

{
    "infra": {
        "storage": { "bucket": "my-bucket", "prefix": "runs/" }
    },
    "train": {
        "output": "{{infra.storage.bucket}}/{{infra.storage.prefix}}model.pt"
    }
}

cfg = ConfigManager()
cfg["output"]   # → "my-bucket/runs/model.pt"

4 — Nested attribute access

When a config value is itself a dict, attribute access returns a namespace object that supports the same interface — including further attribute access, __dir__, len(), and iteration.

{
    "train": {
        "db": { "host": "localhost", "port": 5432 }
    }
}

cfg = ConfigManager()
cfg.db.host          # → "localhost"
cfg.db.port          # → 5432
cfg.db == {"host": "localhost", "port": 5432}   # → True
cfg.db.to_dict()     # → {"host": "localhost", "port": 5432}

5 — Environment variable interpolation

Use ${VAR} in any string value. Variables from the .env file are available too.

{
    "app": {
        "db_url": "postgresql://${DB_USER}:${DB_PASS}@${DB_HOST}/mydb"
    }
}

# config/.env
DB_HOST=localhost
DB_USER=admin
DB_PASS=secret

cfg = ConfigManager()
cfg["db_url"]   # → "postgresql://admin:secret@localhost/mydb"

6 — Logger injection

Pass your own logger to capture config loading events at DEBUG level.

import logging
from refconf_manager import ConfigManager

logging.basicConfig(level=logging.DEBUG)
log = logging.getLogger(__name__)

cfg = ConfigManager(logger=log)
# DEBUG config_manager: Config file: /project/config.json
# DEBUG config_manager: Active section: 'train' | globals: ['root', 'version'] | ...

7 — Override section or root

# Load a specific section explicitly
cfg = ConfigManager(section="shared")

# Start searching from a different directory
cfg = ConfigManager(start_dir="/path/to/project")

Error messages

When a reference can't be resolved, you get a clear, actionable message:

KeyError: "Reference {{preprocess.no_such_key}}: Key 'no_such_key' not found
under 'preprocess'. Available: ['output', 'batch_size']"

KeyError: "Reference {{version}}: no section prefix given and 'version' not
found in '_globals'. Use {{section.version}} or add it to '_globals'."

Config file location

Config files must live inside a config/ directory.
The .env file also goes in the same config/ directory.

project/
├── config/
│   ├── config.json   ← or config.yaml / config.toml
│   └── .env
└── scripts/
    └── train.py

ConfigManager() walks up from the calling script until it finds config/config.json (or yaml/toml).

Config file formats

File	Notes
config/config.json	No extra dependencies
config/config.yaml / config.yml	Requires pip install pyyaml
config/config.toml	Built-in on Python 3.11+; pip install tomli on older

Reference syntax

Use {{section.key}} or {{section.key.subkey.deeper}} in any string value:

{
    "_globals": {"root": "data/"},
    "shared":   {"db": {"host": "localhost", "port": 5432}},
    "app":      {
        "db_url":   "postgresql://{{shared.db.host}}:{{shared.db.port}}/mydb",
        "data_dir": "{{root}}processed/"
    }
}

References work inside nested dicts and lists too.
Bare {{key}} (no dot) is resolved from _globals.

Environment variable syntax

Use ${VAR} to interpolate os.environ values in any string. Substitution happens after {{}} reference resolution, so both syntaxes can coexist:

{
    "app": {
        "host":   "${DB_HOST}",
        "db_url": "postgresql://${DB_USER}@${DB_HOST}/{{_globals.db_name}}"
    }
}

Variables set in config/.env are loaded before interpolation, so they are available as ${VAR} too. A missing variable raises KeyError with a clear message.

API

ConfigManager(section=None, *, start_dir=None, logger=None)

Parameter	Type	Default	Description
section	str	auto-detected	Config section to load
start_dir	str | Path	caller's directory	Where to start searching
logger	logging.Logger	None	Logger for internal debug events

Properties

Property	Returns	Description
section	str	Active section name
config_path	Path	Resolved path to the config file

Dict-like and attribute-style access

cfg["key"]                     # dict-style access (KeyError if missing)
cfg.key                        # attribute-style shorthand (AttributeError if missing)
cfg.get("key", default=None)   # with default
"key" in cfg                   # membership test
len(cfg)                       # number of keys in the active section
for k in cfg: ...              # iterate over keys
cfg.keys() / .values() / .items()
cfg.to_dict()                  # plain dict (recursively unwraps nested namespaces)

Attribute-style access also enables IDE tab-completion: type cfg. and your editor will suggest the keys loaded from the active section (Pylance, Jedi, IPython, Jupyter). Nested dict values return a _Namespace object that supports the same interface, so cfg.db.host and dir(cfg.db) both work.

Note: if a config key shares a name with a built-in method (e.g. get, keys), the method wins on attribute access. Use cfg["get"] in that case.

Note: ConfigManager is read-only — assigning to any public attribute raises AttributeError.

Development

git clone https://github.com/lukaszplk/config-manager
cd config-manager
pip install -e ".[dev]"
pytest

The PyPI package is refconf-manager; the import name is refconf_manager.