multiple-hooks-same-file.md

Registering the same Pluggy hook multiple times in a single file

I found myself wanting to register more than one instance of a Pluggy plugin hook inside a single module.

Hooks are usually registered like this:

@hookimpl
def filters_from_request(request, database, datasette):
    # ...

Where filters_from_request matches the name of a registered plugin hook.

It turns out you can do this instead:

@hookimpl(specname="filters_from_request")
def filters_from_request_1(request, database, datasette):
    # ...

    
@hookimpl(specname="filters_from_request")
def filters_from_request_2(request, database, datasette):
    # ...

Which allows you to write more than one plugin implementation function in the same Python module file.

Note that the specname feature requires Pluggy 1.0.0 or higher.

These can be combined with tryfirst= and trylast=. This example adds one link at the start of the Datasette application menu and one at the end, using the menu_links hook.

from datasette import hookimpl


@hookimpl(specname="menu_links", tryfirst=True)
def menu_links_1(datasette):
    return [
        {"href": datasette.urls.path("/"), "label": "Home"},
    ]


@hookimpl(specname="menu_links", trylast=True)
def menu_links_2():
    return [
        {
            "href": "http://www.example.com/",
            "label": "Link at the end",
        },
    ]