Defaults & Overrides

The configuration system uses three layers that merge in order of precedence:

1. Defaults: values that apply across most usages of an application
2. Configs: values that change or extend the defaults to define a runtime scenario
3. Overrides: values that define exceptions for a specific run, e.g., via command-line arguments

Higher layers override lower layers, allowing flexible configuration composition.

Each layer can load values from one of these sources:

• Files
  Values loaded from YAML files via load_<defaults|config|override> methods.

• Mappings
  Values added from a dict or DictConfig via add_<defaults|config|override> methods.

• Class Field Defaults
  Values parsed from the field defaults of dataclasses or Pydantic models into a DictConfig, then added as a Mapping. See Class Field Defaults for details.

• CLI Arguments
  Values parsed from command-line arguments and options into a DictConfig, then added as a Mapping. See CLI Argument Parsing for details.

While they can be used at any layer, the class field defaults work best when added to the defaults layer, while the CLI arguments work best when added to the overrides layer.