Config Serialization

By default, coma favors YAML over JSON for its config serialization, since omegaconf only supports YAML. However, coma does natively support JSON as well.

Default Behavior

To illustrate the default behavior, let’s revisit an example from the introductory tutorial:

main.py

from dataclasses import dataclass

import coma

@dataclass
class Config:
    message: str = "Hello World!"

if __name__ == "__main__":
    coma.register("greet", lambda cfg: print(cfg.message), Config)
    coma.wake()

Because Config has type name config, it will be serialized to config.yaml by default:

$ python main.py greet
Hello World!
$ cat config.yaml
message: Hello World!

We can force coma to serialize to JSON by specifying an explicit file path for Config:

$ python main.py greet --config-path config.json
Hello World!
$ cat config.json
{
    "message": "Hello World!"
}

Note

By default, coma automatically adds the --config-path flag through the default parser_hook of initiate(). Specifically, a flag of the form --{config_id}-path is added for each global and local config, where {config_id} is the corresponding config identifier.

Now we have two competing config files. Let’s modify each one to distinguish them:

config.yaml

message: Hello YAML!

config.json

{
    "message": "Hello JSON!"
}

Now, if we run the program, we see that YAML is favored:

$ python main.py greet
Hello YAML!

But we can still force coma to use JSON instead:

$ python main.py greet --config-path config.json
Hello JSON!

If we specify a file path without an extension, coma will again favor YAML:

$ python main.py greet --config-path config
Hello YAML!

Finally, if we delete the YAML file while keeping the JSON file, coma will ignore the existing JSON file (and create a new YAML file instead) unless explicitly given a JSON file extension:

$ rm config.yaml
$ python main.py greet --config-path config
Hello World!
$ python main.py greet --config-path config.json
Hello JSON!

In summary, by default coma natively supports JSON, but YAML always takes precedence.

Favoring JSON

We can reverse coma’s default preference by setting JSON as the default file extension through the config_hook of initiate():

main.py

from dataclasses import dataclass

import coma

@dataclass
class Config:
    message: str = "Hello World!"

if __name__ == "__main__":
    coma.initiate(
        config_hook=coma.hooks.config_hook.multi_load_and_write_factory(
            default_ext=coma.config.io.Extension.JSON
        )
    )
    coma.register("greet", lambda cfg: print(cfg.message), Config)
    coma.wake()

First, let’s ensure that both YAML and JSON config files exist and are differentiated:

config.yaml

message: Hello YAML!

config.json

{
    "message": "Hello JSON!"
}

Now, when running the program, we see that JSON is favored in all cases, unless a YAML file extension is explicitly provided:

$ python main.py greet
Hello JSON!
$ python main.py greet --config-path config
Hello JSON!
$ python main.py greet --config-path config.json
Hello JSON!
$ python main.py greet --config-path config.yaml
Hello YAML!