Getting started

Introduction

Hydra is an open-source Python framework that simplifies the development of research and other complex applications. The key feature is the ability to dynamically create a hierarchical configuration by composition and override it through config files and the command line. The name Hydra comes from its ability to run multiple similar jobs - much like a Hydra with multiple heads.

Key features:

• Hierarchical configuration composable from multiple sources
• Configuration can be specified or overridden from the command line
• Dynamic command line tab completion
• Run your application locally or launch it to run remotely
• Run multiple jobs with different arguments with a single command

Versions

Hydra supports Linux, Mac and Windows.
Use the version switcher in the top bar to switch between documentation versions.

	Version	Release notes	Python Versions
►	1.1 (Stable)	Release notes	3.6 - 3.9
	1.0	Release notes	3.6 - 3.8
	0.11	Release notes	2.7, 3.5 - 3.8

Quick start guide

This guide will show you some of the most important features of Hydra. Read the tutorial to gain a deeper understanding.

Installation

pip install hydra-core --upgrade

Basic example

Config:

conf/config.yaml

db:  driver: mysql  user: omry  pass: secret

Application:

my_app.py

import hydrafrom omegaconf import DictConfig, OmegaConf
@hydra.main(config_path="conf", config_name="config")def my_app(cfg : DictConfig) -> None:    print(OmegaConf.to_yaml(cfg))
if __name__ == "__main__":    my_app()

You can learn more about OmegaConf here later.

config.yaml is loaded automatically when you run your application

$ python my_app.pydb:  driver: mysql  pass: secret  user: omry

You can override values in the loaded config from the command line:

$ python my_app.py db.user=root db.pass=1234db:  driver: mysql  user: root  pass: 1234

Composition example

You may want to alternate between two different databases. To support this create a config group named db, and place one config file for each alternative inside: The directory structure of our application now looks like:

├── conf│   ├── config.yaml│   ├── db│   │   ├── mysql.yaml│   │   └── postgresql.yaml│   └── __init__.py└── my_app.py

Here is the new config:

conf/config.yaml

defaults:  - db: mysql

defaults is a special directive telling Hydra to use db/mysql.yaml when composing the configuration object. The resulting cfg object is a composition of configs from defaults with configs specified in your config.yaml.

You can now choose which database configuration to use and override values from the command line:

$ python my_app.py db=postgresql db.timeout=20db:  driver: postgresql  pass: drowssap  timeout: 20  user: postgres_user

You can have as many config groups as you need.

Multirun

You can run your function multiple times with different configuration easily with the --multirun|-m flag.

$ python my_app.py --multirun db=mysql,postgresql[HYDRA] Sweep output dir : multirun/2020-01-09/01-16-29[HYDRA] Launching 2 jobs locally[HYDRA]        #0 : db=mysqldb:  driver: mysql  pass: secret  user: omry
[HYDRA]        #1 : db=postgresqldb:  driver: postgresql  pass: drowssap  timeout: 10  user: postgres_user

There is a whole lot more to Hydra. Read the tutorial to learn more.

Other stuff

Community

Ask questions in the chat or StackOverflow (Use the tag #fb-hydra):

• Zulip Chat
• StackOverflow

Follow Hydra on Twitter and Facebook:

• Facebook page
• Twitter

Citing Hydra

If you use Hydra in your research please use the following BibTeX entry:

@Misc{Yadan2019Hydra,  author =       {Omry Yadan},  title =        {Hydra - A framework for elegantly configuring complex applications},  howpublished = {Github},  year =         {2019},  url =          {https://github.com/facebookresearch/hydra}}