Introduction to Hydra Core

Hydra-core is a powerful framework for elegantly configuring complex applications. It allows developers to compose configurations dynamically, making it easier to manage diverse configuration scenarios for different environments and stages of development.

Main Features and APIs

Here are some of the key APIs and features of Hydra-core:

@hydra.main()

The @hydra.main() decorator is the entry point for running a Hydra-configured application.

  
    from hydra import main

    @main(config_name="config")
    def my_app(cfg):
        print(cfg.pretty())
  

OmegaConf

Hydra leverages OmegaConf for configuration composition and manipulation.

  
    from omegaconf import OmegaConf
    
    config = OmegaConf.create({"db": {"host": "localhost", "port": 5432}})
    print(config.db.host)  # Outputs: localhost
  

hydra.utils.to_absolute_path()

Convenient utility to work with file systems, converting relative paths to absolute paths.

  
    import hydra
    from hydra.utils import to_absolute_path
    
    @hydra.main(config_name="config")
    def my_app(_cfg):
        print(to_absolute_path("my_relative_path"))
  

hydra.run()

Directly launching the application defined using Hydra.

  
    from hydra.experimental import compose, initialize
    initialize(config_path="conf")
    config = compose(config_name="config")
    print(config)
  

Application Example

Let’s build a simple example application that uses several Hydra-core features:

  
    # my_app.py

    import hydra
    from hydra.utils import to_absolute_path
    from omegaconf import DictConfig
    
    @hydra.main(config_name="config")
    def my_app(cfg: DictConfig):
        db_host = cfg.database.host
        db_port = cfg.database.port
        file_path = to_absolute_path(cfg.file_path)
        print(f"Connecting to database at {db_host}:{db_port}")
        print(f"Processing file at {file_path}")

    if __name__ == "__main__":
        my_app()
  

Assuming the configuration file config.yaml contains:

  
    database:
      host: localhost
      port: 5432
    file_path: "data/example.txt"
  

Running the script will produce:

  
    $ python my_app.py
    Connecting to database at localhost:5432
    Processing file at /absolute/path/to/data/example.txt
  

Hydra-core makes managing complex configurations simple and clean, enabling developers to focus on application logic.

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