{"id": "writing_plugins:writing-plugins-extra-hooks", "page": "writing_plugins", "ref": "writing-plugins-extra-hooks", "title": "Plugins that define new plugin hooks", "content": "Plugins can define new plugin hooks that other plugins can use to further extend their functionality. \n             datasette-graphql  is one example of a plugin that does this. It defines a new hook called  graphql_extra_fields ,  described here , which other plugins can use to define additional fields that should be included in the GraphQL schema. \n             To define additional hooks, add a file to the plugin called  datasette_your_plugin/hookspecs.py  with content that looks like this: \n             from pluggy import HookspecMarker\n\nhookspec = HookspecMarker(\"datasette\")\n\n\n@hookspec\ndef name_of_your_hook_goes_here(datasette):\n    \"Description of your hook.\" \n             You should define your own hook name and arguments here, following the documentation for  Pluggy specifications . Make sure to pick a name that is unlikely to clash with hooks provided by any other plugins. \n             Then, to register your plugin hooks, add the following code to your  datasette_your_plugin/__init__.py  file: \n             from datasette.plugins import pm\nfrom . import hookspecs\n\npm.add_hookspecs(hookspecs) \n             This will register your plugin hooks as part of the  datasette  plugin hook namespace. \n             Within your plugin code you can trigger the hook using this pattern: \n             from datasette.plugins import pm\n\nfor (\n    plugin_return_value\n) in pm.hook.name_of_your_hook_goes_here(\n    datasette=datasette\n):\n    # Do something with plugin_return_value\n    pass \n             Other plugins will then be able to register their own implementations of your hook using this syntax: \n             from datasette import hookimpl\n\n\n@hookimpl\ndef name_of_your_hook_goes_here(datasette):\n    return \"Response from this plugin hook\" \n             These plugin implementations can accept 0 or more of the named arguments that you defined in your hook specification.", "breadcrumbs": "[\"Writing plugins\"]", "references": "[{\"href\": \"https://github.com/simonw/datasette-graphql\", \"label\": \"datasette-graphql\"}, {\"href\": \"https://github.com/simonw/datasette-graphql/blob/main/README.md#adding-custom-fields-with-plugins\", \"label\": \"described here\"}, {\"href\": \"https://pluggy.readthedocs.io/en/stable/#specs\", \"label\": \"Pluggy specifications\"}]"}