Config

This module provides base a class for configs that can be loaded from files, environment variables or command line arguments.

Creating and loading configs

Derive your config from the Config base class. Inside of its body, define config fields using type annotations. This is similar to how you create dataclasses:

class AppConfig(Config):
    app_version: str
    deployment_strategy: str = 'ROLLING'

Config defines __init__ that takes keyword arguments for defined fields, as well as some constructors that load config from environment variables, files, and so on.

Upon creation, all fields that aren’t explicitly initialized and don’t have defaults are considered missing. Accessing them will raise AttributeError.

Here’s an example of loading our config from command line arguments and environment variables:

# Load config from env.
config = AppConfig.load_from_env()

# Create and setup parser.
parser = argparse.ArgumentParser()
AppConfig.setup_parser(parser)

# Parse arguments, convert them to config,
# and merge with config loaded from env.
config.update(AppConfig.load_from_args(parser.parse_args()))

class yuio.config.Config(**kwargs)

Base class for configs.

update(other: _Self)

Update fields in this config with fields from another config.

This function is similar to dict.update().

classmethod load_from_env() → _Self

Load config from environment variables.

Use Config.update() to merge several loaded configs into one.

classmethod load_from_args(args: Optional[Namespace] = None) → _Self

Load config from parsed command line arguments.

This method assumes that arguments parser was configured with Config.setup_parser().

Use Config.update() to merge several loaded configs into one.

If args is not given, will create a parser and parse arguments from sys.argv.

classmethod load_from_config(config: Dict[str, Any], ignore_unknown_fields: bool = False) → _Self

Load config from parsed config file.

This method takes a dict with arbitrary values that resulted from parsing type-rich configs such as .yaml or .json.

For example:

with open('conf.yml') as file:
    config = Config.load_from_config(yaml.load(file))

Use Config.update() to merge several loaded configs into one.

classmethod load_from_json(path: str, ignore_unknown_fields: bool = False)

Load config from a .json file.

classmethod setup_parser(parser: Optional[ArgumentParser] = None) → ArgumentParser

Add fields from this config as flags to an argparse parser.

If parser is not given, will create one.

Advanced field configuration

By default, Config infers names for env variables and flags, appropriate parsers, and other things from field’s name and type hint. If you need to override them, theres the field() function:

class AppConfig(Config):
    app_version: str = field(
        default='HEAD',
        help='git tag or commit hash at which a new version is built.',
    )
    deployment_strategy: str = field(
        default='ROLLING',
        help='strategy that will be used to deploy new pods.',
        parser=yuio.parse.OneOf(
            yuio.parse.StrUpper(),
            ['ROLLING', 'READONLY', 'DOWNTIME']
        )

yuio.config.field(*, help: Optional[str] = 'None', env: Optional[str] = 'None', flag: Optional[Union[str, List[str]]] = 'None') → Any

yuio.config.field(default: T = _MISSING, *, parser: Parser[T], help: Optional[str] = 'None', env: Optional[str] = 'None', flag: Optional[Union[str, List[str]]] = 'None') → T

Field descriptor, used for additional configuration of fields.

This is similar to what dataclasses.field() does.

Parameters

• default – default value for config field, used if field is missing from config.

• parser – parser that will be used to parse env vars, configs and CLI arguments. By default, it’s inferred from type hint.

• help – help message that will be used in CLI argument description.

• env – name of environment variable that will be used for this field. By default, it’s inferred from field name. Set to disabled() to disable parsing from environment variable.

• flag – name of a CLI flag (or a list of names) that will be used for this field. By default, it’s inferred from field name. Set to disabled() to disable parsing from command line arguments.

yuio.config.disabled() → Any

Placeholder indicating that some field’s functionality is disabled.

Example:

class AppConfig(Config):
    app_version: str = field(env=disabled())