testbed/facebookresearch__hydra/website/docs/intro.md

metadata

id: intro
title: Getting started
sidebar_label: 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.

	Version	Docs	Release notes	Python Version
	0.11 (Stable)	0.11 Docs	Release notes	2.7, 3.5+
►	1.0 (Release candidate)	1.0 docs	Release notes	3.6+

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

Install Hydra 1.0 with pip install hydra-core --pre --upgrade.
This version may contain nuts and bugs and might be incompatible with existing plugins.

Basic example

Config:

db:
  driver: mysql
  user: omry
  pass: secret

Application:

import hydra
from omegaconf import DictConfig

@hydra.main(config_name="config")
def my_app(cfg : DictConfig) -> None:
    print(cfg.pretty())

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.py
db:
  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=1234
db:
  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:

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

Here is the new config:

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 from the and override values from the command line:

$ python my_app.py db=postgresql db.timeout=20
db:
  driver: postgresql
  pass: drowssap
  timeout: 20
  user: postgre_user
website:
  domain: example.com

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=mysql
db:
  driver: mysql
  pass: secret
  user: omry
website:
    domain: example.com

[HYDRA]        #1 : db=postgresql
db:
  driver: postgresql
  pass: drowssap
  timeout: 10
  user: postgre_user
website:
    domain: example.com

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