testbed/facebookresearch__hydra/website/docs/advanced/overriding_packages.md

metadata

id: overriding_packages
title: Overriding packages

The contents of a config file can be relocated, or replicated, within the config, via package overrides.

Package specification

PACKAGE      : _global_ | COMPONENT[.COMPONENT]*
COMPONENT    : _group_ | _name_ | \w+

_global_     : the top level package (equivalent to the empty string).
_group_      : the config group in dot notation: foo/bar/zoo.yaml -> foo.bar
_name_       : the config file name: foo/bar/zoo.yaml -> zoo

Overriding the package in a file via a package directive

A @package directive specifies a common package for all nodes in the config file. It must be placed at the top of each config group file.

# @package foo.bar
# @package _global_
# @package _group_
# @package _group_._name_
# @package foo._group_._name_

Examples

A package directive with a literal

# @package foo.bar

db:
  host: localhost
  port: 3306

foo:
  bar:
    db:
      host: localhost
      port: 3306

A package directive with _group_ and _name_

# @package _group_._name_

host: localhost
port: 3306

db:
  mysql:
    host: localhost
    port: 3306

Overriding the package via the defaults list

The following example adds the mysql config in under the packages src and dst.

defaults:
 - db@db.src: mysql
 - db@db.dst: mysql

db:
  src:
    host: localhost
    port: 3306
  dst:
    host: localhost
    port: 3306

Overriding the package via the command line

Overriding the package for db specified in the defaults list from db.dst to backup:

$ python my_app.py db@db.dst:backup
$ python my_app.py db@db.dst:backup=postgresql # And change the config group option

Overriding the package of a config group option not in the defaults list:

python my_app.py +webserver@prod=apache

For more details, see the Command line overrides page.

History and future of the package directive

The primary config, named in @hydra.main() should not have a package directive.

For config files in config groups the default depends on the version:

• In Hydra 0.11, there was an implicit default of _global_
• Hydra 1.0 the default is _global_
  A warning is issued for each config group file without a @package directive.
• In Hydra 1.1 the default for config group files will become _group_

By adding an explicit @package to your configs files, you guarantee that they
will not break when you upgrade to Hydra 1.1.