Specifying a config file

 

It can get tedious to type all those command line arguments. You can solve it by creating a configuration file next to my_app.py. Hydra configuration files are yaml files and should have the .yaml file extension.

config.yaml

db: 
  driver: mysql
  user: omry
  password: secret

Specify the config name by passing a config_name parameter to the @hydra.main() decorator. Note that you should omit the .yaml extension. Hydra also needs to know where to find your config. Specify the directory containing it relative to the application by passing config_path:

my_app.py

from omegaconf import DictConfig, OmegaConf
import hydra

@hydra.main(config_path=".", config_name="config")
def my_app(cfg):
    print(OmegaConf.to_yaml(cfg))

if __name__ == "__main__":
    my_app()

config.yaml is loaded automatically when you run your application.

$ python my_app.py
db:
  driver: mysql
  user: omry
  password: secret

You can override values in the loaded config from the command line.
Note the lack of the + prefix.

$ python my_app.py db.user=root db.password=1234
db:
  driver: mysql
  user: root
  password: 1234

Use ++ to override a config value if it's already in the config, or add it otherwise. e.g:

# Override an existing item
$ python my_app.py ++db.password=1234

# Add a new item
$ python my_app.py ++db.timeout=5

You can enable tab completion for your Hydra applications.