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Version: 1.0

strict flag mode deprecation

Overview​

The strict mode is a flag added to @hydra.main() to enable two features:

  • Command line error detection (overriding a field not in the config)
  • Runtime config access error detection (accessing/setting a field not in the config)

This flag is now deprecated and the ability to turn it off will be removed in Hydra 1.1.

Alternatives to strict=False​

Below are a few common reasons for people disabling strict mode along with recommended alternatives.

Adding config fields through the command line​

With strict mode disabled; you can add fields not specified in config file through the command line. Hydra 1.0 introduces the + prefix to command line overrides, enabling the addition of fields not in the config file.

config.yaml
db:
  driver: mysql
$ python my_app.py +db.host=localhost
db:
  driver: mysql
  host: localhost

Adding fields at runtime​

When strict mode is disabled, you can add fields to your config at runtime. Strict mode is implemented by setting the OmegaConf struct flag to True on the root of the config.

  • You can disable the struct flag a specific context using open_dict.
  • You can disable the struct flag permanently for your config using OmegaConf.set_struct(cfg, False).

Learn more about OmegaConf struct flag here.

Field existence check​

With strict mode disabled, you can check if a field is in the config by comparing it to None:

if cfg.host is None:
    # host is not in the config

This will no longer work because an exception will be thrown when the host field is accessed.
Use in or hasattr instead:

if "host" not in cfg:
    # host is not in the config

if not hasattr(cfg, "host"):
    # host is not in the config