module.server

module.server(fn)

Decorator for defining a Shiny module server function.

A Shiny module is a reusable component that can be embedded within Shiny apps or other Shiny modules. Each module consists of a UI function and a server function. This decorator is used to encapsulate the server logic for a Shiny module.

Every Shiny module server function must always begin with the same three arguments: input, output, and session, just like a Shiny app's server function.

After input, output, and session, the server function may include additional parameters to be used in the server logic; for example, reactive data sources or file paths that need to be provided by the caller.

This decorator modifies the signature of the decorated server function. The input, output, and session parameters are removed, and a new id parameter is prepended to the signature.

This decorator is used to encapsulate the server logic for a Shiny module. It automatically creates a namespaced child Session using the provided module id, and passes the appropriate input, output, and session objects to your server function.

This ensures that the server logic is scoped correctly for each module instance and allows for reuse of logic across multiple instances of the same module.

Parameters

fn : Callable[Concatenate[Inputs, Outputs, Session, P], R]

A server function that takes input, output, and session as its first three arguments, followed by any additional arguments defined by the user.

Returns

: Callable[Concatenate[str, P], R]

The decorated server function. A function that takes a module id (as a string) as its first argument, followed by any arguments expected by fn. When called, it will register the module’s server logic in a namespaced context. The function signature of fn will have been modified to remove input, output, and session, and to prepend a new id parameter.

See Also

• Shiny Modules documentation: https://shiny.posit.co/py/docs/modules.html
• shiny.module.ui

Examples

#| standalone: true
#| components: [editor, viewer]
#| layout: vertical
#| viewerHeight: 400

## file: app.py
from shiny import App, Inputs, Outputs, Session, module, reactive, render, ui


# ============================================================
# Counter module
# ============================================================
@module.ui
def counter_ui(label: str = "Increment counter") -> ui.TagChild:
    return ui.card(
        ui.h2("This is " + label),
        ui.input_action_button(id="button", label=label),
        ui.output_text(id="out"),
    )


@module.server
def counter_server(
    input: Inputs, output: Outputs, session: Session, starting_value: int = 0
):
    count: reactive.value[int] = reactive.value(starting_value)

    @reactive.effect
    @reactive.event(input.button)
    def _():
        count.set(count() + 1)

    @render.text
    def out() -> str:
        return f"Click count is {count()}"


# =============================================================================
# App that uses module
# =============================================================================
app_ui = ui.page_fluid(
    counter_ui("counter1", "Counter 1"),
    counter_ui("counter2", "Counter 2"),
)


def server(input: Inputs, output: Outputs, session: Session):
    counter_server("counter1")
    counter_server("counter2")


app = App(app_ui, server)