I'd like to add a key + value after my Hydra Config is loaded. Essentially I want to run my code and check if a gpu is available or not. If it is, log the device as gpu, else keep the cpu.

Essentially saving the output of :

torch.cuda.is_available()

When I try to add a key with "setdefault" as such:

@hydra.main(config_path="conf", config_name="config")
def my_app(cfg: DictConfig) -> None:
    cfg.setdefault("new_key", "new_value")

Same error if I do:

  cfg.new_key = "new_value"
  print(cfg.new_key)

I get the error:

omegaconf.errors.ConfigKeyError: Key 'new_key' is not in struct
        full_key: new_key
        reference_type=Optional[Dict[Union[str, Enum], Any]]
        object_type=dict

My current workaround is to just use OmegaConfig as such:

  cfg = OmegaConf.structured(OmegaConf.to_yaml(cfg))
  cfg.new_key = "new_value"
  print(cfg.new_key)
  >>>> new_value

Surely there must be a better way to do this?

Hydra sets the struct flag on the root of the OmegaConf config object it produces. See this for more info about the struct flag.

You can use open_dict() to temporarily disable this and to allow the addition of new keys:

>>> from omegaconf import OmegaConf,open_dict
>>> conf = OmegaConf.create({"a": {"aa": 10, "bb": 20}})
>>> OmegaConf.set_struct(conf, True)
>>> with open_dict(conf):
...   conf.a.cc = 30
>>> conf.a.cc
30