Hydra: How to express None in config files?

Question

I have a very simple Python script:

import hydra
from omegaconf import DictConfig, OmegaConf


@hydra.main(version_base="1.3", config_path=".", config_name="config")
def main(cfg: DictConfig) -> None:
    if cfg.benchmarking.seed_number is None: 
        raise ValueError()

if __name__ == "__main__": 
    main()

And here the config file:

benchmarking: 
  seed_number: None 

Unfortunately, the Python script does not raise an error. Instead, when I print the type of cfg.benchmarking.seed_number, it is str. How can I pass None instead?

Proprietary

What value is cfg.benchmarking.seed_number being set to? "None" or something else? Does hydra document how it's config (yaml?) file is parsed? – Mariettemarigold

You should use the word 'null' instead of None in the configuration file – Ballottement

Answer 1

Try null:

benchmarking: 
  seed_number: null

Harriet

Thanks - I've been using this stuff for years and didn't think you could! – Kellar

Answer 2

In YAML format, it represents None as a string ("None").

To pass None as the value instead, you can replace it with !!null

benchmarking:
seed_number: !!null

Using !!null in the YAML configuration, it explicitly represents a null value.

But as this configuration is loaded into the Python, cfg.benchmarking.seed_number will be None instead of a string.

Pupillary

Answer 3

As mentioned at https://omegaconf.readthedocs.io/en/latest/grammar.html

Other special keywords (also case-independent): null, true, false, NULL, True, fAlSe. IMPORTANT: None is not a special keyword and will be parsed as an unquoted string, you must use the null keyword instead (as in YAML).

in my Hydra setup both null and !!null worked. !!null is more distinctive to the developer eye :) .

Audio