How to dump a hydra config into yaml with `_target_` fields

Question

I instantiate a hydra configuration from a python dataclass. For example

from dataclasses import dataclass
from typing import Any
from hydra.utils import instantiate

class Model():
    def __init__(self, x=1):
        self.x = x

@dataclass
class MyConfig:
    model: Any
    param: int

static_config = MyConfig(model=Model(x=2), param='whatever')
instantiated_config = instantiate(static_config)

Now, I would like to dump this configuration as a yaml, including the _target_ fields that Hydra uses to re-instantiate the objects pointed to inside the configuration. I would like to avoid having to write my own logic to write those _target_ fields, and I imagine there must be some hydra utility that does this, but I can't seem to find it in the documentation.

Answer 1

See OmegaConf.to_yaml and OmegaConf.save:

from omegaconf import OmegaConf

# dumps to yaml string
yaml_data: str = OmegaConf.to_yaml(my_config)

# dumps to file:
with open("config.yaml", "w") as f:
    OmegaConf.save(my_config, f)

# OmegaConf.save can also accept a `str` or `pathlib.Path` instance:
OmegaConf.save(my_config, "config.yaml")

See also the Hydra-Zen project, which offers automatic generation of OmegaConf objects (which can be saved to yaml).