tnm-config 1.3.1

Small config loader supporting YAML, JSON and XML with env support.

tnm-config

A lightweight configuration loader for Python. Supports YAML, JSON, XML (and is pluggable for other formats). Features environment-backed values, filesystem paths, optional typed validation (Pydantic models or dataclasses), and a loader registry for plugins.

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Install

Basic

pip install tnm-config

Optional extras:

pip install "tnm-config[yaml]"     # PyYAML support
pip install "tnm-config[xml]"      # xmltodict support
pip install "tnm-config[all]"      # yaml + xml + pydantic extras (if provided)

If you want schema_type validation with Pydantic models:

pip install pydantic

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Quick API

Import:

from pathlib import Path
from tnm.config import ConfigLoader
from tnm.config.errors import ConfigError

Basic usage:

loader = ConfigLoader(Path("config/example_config.yaml"))

# Raw resolved dict/list/scalar
cfg = loader.load("elasticsearch", project_root_callback=lambda: Path.cwd())

# With schema (pydantic model or dataclass):
cfg_obj = loader.load("elasticsearch", project_root_callback=lambda: Path.cwd(), schema_type=MyModel)

Type hint behaviour:

• If schema_type is None: return is a parsed JSON-like type (dict | list | str | int | ...).
• If schema_type supplied: return is schema_type.

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Supported file marker syntax

Environment-backed values

These let you source values from environment variables with a type hint.

YAML:

hosts: !env [ ES_HOSTS, list:url, http://127.0.0.1:9200 ]

JSON:

"hosts": { "__env__": ["ES_HOSTS", "list:url", "http://127.0.0.1:9200"] }

XML:

<hosts>
  <env var="ES_HOSTS" type="list:url" default="http://127.0.0.1:9200"/>
</hosts>

Supported casts:

• str, int, float, bool
• url (validates that parsed URL has scheme + host)
• list:str, list:url (comma separated values)

If env var not set and no default provided, a EnvVarNotSetError is raised.

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Project-relative paths & preserved tokens

YAML !path and JSON/XML mapping variants are supported.

YAML:

templates_dir: !path extras/templates

JSON:

"templates_dir": { "__path__": { "value": "extras/templates" } }

XML:

<templates_dir>
  <path value="extras/templates"/>
</templates_dir>

Preserved tokens inside strings are supported in both %token% and {{ token }} forms:

• %project_root%, %project_dir%, {{ project_root }} resolved via caller project_root_callback().
• %home%, %user_home%, {{ home }} the current OS user's home directory
• %user%, %username%, {{ user }} same as home token

You can mix tokens with path fragments:

templates_dir: "%project_root%/extras/templates"
local_cache: "{{ home }}/.myapp/cache"

You may also use an explicit mapping form (recommended for JSON/XML):

"templates_dir": {
  "__path__": {
    "value": "{{project_root}}/data/json/es_queries"
  }
}

Important: when resolving tokens that require the project's root (e.g. %project_root%) you must pass a zero-argument callable project_root_callback to load(...). Example:

cfg = loader.load("elasticsearch", project_root_callback=lambda: Path.cwd())

If a token requires the project root but you didn't provide the callback, ConfigError will be raised with a helpful message.

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Example config files

YAML (example_config.yaml):

elasticsearch:
  hosts: !env [ ES_HOSTS, list:url, http://127.0.0.1:9200 ]
  username: !env [ ES_USERNAME, str, demo_user ]
  password: !env [ ES_PASSWORD, str, demo_pass ]
  templates_dir: !path "{{project_root}}/extras/templates"
  timeout: 10
  version: 8.15

JSON (example_config.json):

{
  "elasticsearch": {
    "hosts": { "__env__": ["ES_HOSTS", "list:url", "http://127.0.0.1:9200"] },
    "username": { "__env__": ["ES_USERNAME", "str", "demo_user"] },
    "password": { "__env__": ["ES_PASSWORD", "str", "demo_pass"] },
    "templates_dir": { "__path__": { "value": "{{project_root}}/extras/templates" } },
    "timeout": 10,
    "version": 8.15
  }
}

XML (example_config.xml):

<?xml version="1.0" encoding="utf-8"?>
<elasticsearch>
    <hosts>
        <env var="ES_HOSTS" type="list:url" default="http://127.0.0.1:9200"/>
    </hosts>
    <username>
        <env var="ES_USERNAME" type="str" default="demo_user"/>
    </username>
    <password>
        <env var="ES_PASSWORD" type="str" default="demo_pass"/>
    </password>
    <templates_dir>
        <path value="{{project_root}}/extras/templates"/>
    </templates_dir>
    <timeout>10</timeout>
    <version>8.15</version>
</elasticsearch>

All three examples are semantically equivalent. Scalar values (numbers, strings, booleans) may be present anywhere and will be returned as-is.

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Typed schemas (validation)

You can pass a schema_type to load(...). Supported schema types:

• Pydantic BaseModel.
• Plain Python dataclass.
• Any callable/class that accepts the resolved dict or scalar in its constructor.

from pydantic import BaseModel
from tnm.config import ConfigLoader

class ElasticCfg(BaseModel):
    hosts: list[str]
    username: str | None = None
    password: str | None = None
    templates_dir: str | None = None

loader = ConfigLoader(Path("config/example_config.yaml"))
cfg_obj = loader.load("elasticsearch", project_root_callback=lambda: Path.cwd(), schema_type=ElasticCfg)

If validation fails, a ConfigError is raised (with the underlying validation exception as __cause__).

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Loader registry & plugin entry-point

There is a loader registry so additional formats can be added.

Runtime registration:

from tnm.config.loaders import register_loader, get_loader_for_suffix

register_loader(".ini", lambda: MyIniLoader())
loader = get_loader_for_suffix(".ini")
data = loader.load(Path("config.ini"), project_root_callback=lambda: Path.cwd())

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Errors & exceptions

All package-specific exceptions are subclasses of tnm.config.errors.ConfigError.

Key exceptions:

• ConfigError – generic parse/resolve/validation error (base).
• EnvVarNotSetError – env var referenced by !env/__env__/<env/> is not set and no default provided.
• InvalidURLError – env var declared as url is invalid.

Usage:

from tnm.config import ConfigLoader, ConfigError

try:
    cfg = ConfigLoader(Path("config.yaml")).load("elasticsearch", project_root_callback=my_cb)
except ConfigError as exc:
    # inspect exc.__cause__ for underlying error details (if any)
    print("Config failed:", exc)

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Security & safety

• YAML parsing uses safe_load and custom safe constructors. Do not parse untrusted YAML.
• Be cautious with logging or printing secrets from config (passwords, tokens).
• When using schema_type, underlying validation errors are preserved in __cause__ to help debugging — avoid leaking them to users.

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Using preserved tokens:

es.yaml:

elasticsearch:
  templates_dir: "%project_root%/extras/templates"
  backup_dir: "{{ home }}/.cache/myapp/backups"

Load:

cfg = ConfigLoader(Path("es.yaml")).load("elasticsearch", project_root_callback=lambda: Path("/srv/myclient"))

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Contributing & roadmap

Possible next steps:

• Add dacite optional extra for full dataclass support (nested dataclasses).
• Add tnm-config-validate CLI to validate a config against a schema.
• Add caching for parsed config and file watch invalidation.
• Add small JSON Schema adapter for validating raw config shapes.

Contributions via PRs are welcome.

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License

MIT