[Feature request] Load YAML with BASE config

[qizhuli]

Allow constructing a new config file based on an existing one

This feature has been implemented in the config class in repo facebookresearch/fvcore, which uses a special key _BASE_ to specify a base config file.

Such a feature improves the maintainability of large number of similar config files, and helps highlight the difference between similar configs.

Would like to hear your opinion on this. Many thanks.

[vakker]

That would make YACS really great, another example is the MMCV config parser. I would assume that it's relatively simple to implement, e.g. something like:

cfg = get_cfg_defaults()
cfg.merge_from_file("experiment.yaml")

for base_file in cfg._BASE_:
    cfg.merge_from_file(base_file)

Maybe the order or merging should be the other way around?