Skip to main content
Version: 1.0

Defaults List

 Example

You can define a defaults list in your primary Structured Config just like you can in your primary config.yaml file. The example below extends the previous example by adding a defaults list that will load db=mysql by default.


from omegaconf import MISSING, OmegaConf  # Do not confuse with dataclass.MISSING
@dataclassclass MySQLConfig:    ...
@dataclassclass PostGreSQLConfig:    ...
defaults = [    # Load the config "mysql" from the config group "db"    {"db": "mysql"}]
@dataclassclass Config:    # this is unfortunately verbose due to @dataclass limitations    defaults: List[Any] = field(default_factory=lambda: defaults)
    # Hydra will populate this field based on the defaults list    db: Any = MISSING
cs = ConfigStore.instance()cs.store(group="db", name="mysql", node=MySQLConfig)cs.store(group="db", name="postgresql", node=PostGreSQLConfig)cs.store(name="config", node=Config)

@hydra.main(config_name="config")def my_app(cfg: Config) -> None:    print(OmegaConf.to_yaml(cfg))

if __name__ == "__main__":    my_app()

Running my_app.py loads the mysql config option by default:

$ python my_app.pydb:  driver: mysql  ...

You can override the default option via the command line:

$ python my_app.py db=postgresqldb:  driver: postgresql  ...

Requiring users to specify a default list value#

Set db as MISSING to require the user to specify a value on the command line.

Defaults list with a missing db
defaults = [    {"db": MISSING}]

Output
$ python my_app.pyYou must specify 'db', e.g, db=<OPTION>Available options:        mysql        postgresql