ApPySetty ⚙️

A simple, type-safe Python library for managing application configuration from environment variables and YAML.

ApPySetty uses Python dataclasses as the single definition of your application configuration. It can load values from configuration files and environment variables and generate documentation from the same definition.

Quick Start

Install:

uv add appysetty

Define your configuration:

from dataclasses import dataclass

from appysetty import AppConfigSource, read_configuration


@dataclass
class Config:
    host: str = "localhost"
    port: int = 8080
    debug: bool = False


config = read_configuration(
    Config,
    AppConfigSource.ENV,
)

Override values with environment variables:

export HOST="0.0.0.0"
export PORT="9000"
export DEBUG="true"

Or load them from YAML:

host: localhost
port: 8080
debug: false

config = read_configuration(
    Config,
    AppConfigSource.YAML,
)

And also document your configuration with an example yaml and a markdown document:

write_configuration_documentation(Config, output_dir=Path("./docs"))

Configuration Sources

ApPySetty currently supports:

• ENV: environment variables using UPPER_SNAKE_CASE only
• YAML: YAML configuration files

Multiple sources can be combined. Later sources overwrite values from earlier sources:

config = read_configuration(
    Config,
    [
        AppConfigSource.YAML,
        AppConfigSource.ENV,
    ],
)

By default, YAML files are searched for in:

config.yaml
config.yml
config/config.yaml
config/config.yml

An explicit YAML path can also be provided.

Usage Details

Define Config

First you need to define a dataclass which contains all the configuration options you want to support.

@dataclass
class Config:
    host: str = "localhost"
    port: int = 8080
    debug: bool = False
    timeout: float = 5.0

You can also extend your dataclass with additional information for better documentation and for masking secrets:

@dataclass
class ConfigWithMetadata:
    host: Annotated[
        str,
        AppConfigEntry(description="The application host"),
    ] = "localhost"

    password: Annotated[
        str,
        AppConfigEntry(description="The database password", is_secret=True),
    ] = "secret"

Both variants can be mixed. If no description is provided, the name of the field will be the description.

Read Config

To read the config, use:

cfg = read_configuration(ConfigWithMetadata, AppConfigSource.ENV)

After that cfg should have all configurations with auto-complete ready for you.

You can also pass an instance and use multiple sources, where each source will overwrite the previous one:

cfg = read_configuration(
    ConfigWithMetadata(), [AppConfigSource.ENV, AppConfigSource.YAML]
)

The available sources are:

Options

Options can be used to customize the config:

cfg = read_configuration(
    ConfigWithMetadata,
    [AppConfigSource.ENV, AppConfigSource.YAML],
    AppConfigOptions(
        env_prefix="MY_APP_PREFIX",
        yaml_path="config.dev.yaml",
        overwrite={"port": "8000"},
    ),
)

Write Documentation

The second feature of this tool is automated creation of a few documentation items for configuration options:

• config.example.yaml containing an example yaml file with default values and descriptive comments (if descriptions were defined)
• DefaultConfiguration.md containing a table of all options with ENV variant, a docker environment block for docker compose and a docker run example command with all -e set.

To create the documentation, use:

# Create both documents
write_configuration_documentation(
    ConfigWithMetadata, env_prefix="MY_APP_PREFIX", output_dir=Path()
)

# Only create yaml example
write_config_yaml_example(ConfigWithMetadata, output_dir=Path())

# Only create markdown document
write_config_markdown(ConfigWithMetadata, env_prefix="MY_APP_PREFIX", output_dir=Path())

Development

Clone the repository and install the development dependencies:

git clone https://github.com/SmartFactory-KL/appysetty.git
cd appysetty
uv sync

Run the tests:

uv run pytest

Run tests with coverage:

uv run pytest --cov=appysetty --cov-report=term-missing

Run the examples:

uv run python -m examples.write_documentation
uv run python -m examples.read_documentation

License

ApPySetty is licensed under the MIT License.