| --- |
| id: plugins |
| title: Hydra plugins types |
| sidebar_label: Hydra plugins |
| --- |
| |
| Hydra can be extended via plugins. |
| You can see example plugins [here](https://github.com/facebookresearch/hydra/tree/master/plugins/examples). |
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| <div class="alert alert--info" role="alert"> |
| <strong>NOTE</strong>: |
| If you develop plugins, please join the <a href="https://hydra-framework.zulipchat.com/#narrow/stream/233935-Hydra-plugin.20dev.20announcements">plugin developer announcement channel</a> in the chat. |
| </div> |
| <br/> |
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| ## Plugin discovery |
| The plugin discovery process runs whenever Hydra starts. During plugin discovery, Hydra scans for plugins in all the submodules of `hydra_plugins`. Hydra will import each module and look for plugins defined in that module. |
| Any module under `hydra_plugins` that is slow to import will slow down the startup of _ALL_ Hydra applicaitons. |
| Plugins with expensive imports can exclude individual files from this by prefixing them with `_` (but not `__`). |
| For example, the file `_my_plugin_lib.py` would not be imported and scanned, while `my_plugin_lib.py` would be. |
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| ## Plugin types |
| ### Sweeper |
| A sweeper is responsible for converting command line arguments list into multiple jobs. |
| For example, the basic built-in sweeper takes arguments like: |
| ``` |
| batch_size=128 optimizer=nesterov,adam learning_rate=0.01,0.1 |
| ``` |
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| And creates 4 jobs with the following parameters: |
| ``` |
| batch_size=128 optimizer=nesterov learning_rate=0.01 |
| batch_size=128 optimizer=nesterov learning_rate=0.1 |
| batch_size=128 optimizer=adam learning_rate=0.01 |
| batch_size=128 optimizer=adam learning_rate=0.1 |
| ``` |
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| ### Launcher |
| Launchers are responsible for launching a job to a specific environment. |
| A Launcher is taking a batch of argument lists like the one above and launches a job for each one. |
| The job uses those arguments to compose its configuration. |
| The basic launcher simply launches the job locally. |
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| ### SearchPathPlugin |
| A config path plugin can manipulate the search path. |
| This can be used to influence the default Hydra configuration to be more appropriate to a specific environment, |
| or just add new entries to the search path to make more configurations available to the Hydra app. |
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| SearchPathPlugin plugins are discovered automatically by Hydra and are being called to manipulate the search path before |
| the configuration is composed. |
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| Many other plugins also implement SearchPathPlugin to add their configuration to the config search path once they are installed. |
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| ### ConfigSource |
| ConfigSource plugins can be used to allow Hydra to access configuration in non-standard locations when composing the config. |
| This can be used to enable to access an in-house private config store, or as a way to access configs from public sources like GitHub or S3. |
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