testbed/Textualize__textual/docs/examples/guide/reactivity/validate01.py

from textual.app import App, ComposeResult
from textual.containers import Horizontal
from textual.reactive import reactive
from textual.widgets import Button, TextLog


class ValidateApp(App):
    CSS_PATH = "validate01.css"

    count = reactive(0)

    def validate_count(self, count: int) -> int:
        """Validate value."""
        if count < 0:
            count = 0
        elif count > 10:
            count = 10
        return count

    def compose(self) -> ComposeResult:
        yield Horizontal(
            Button("+1", id="plus", variant="success"),
            Button("-1", id="minus", variant="error"),
            id="buttons",
        )
        yield TextLog(highlight=True)

    def on_button_pressed(self, event: Button.Pressed) -> None:
        if event.button.id == "plus":
            self.count += 1
        else:
            self.count -= 1
        self.query_one(TextLog).write(f"{self.count=}")


if __name__ == "__main__":
    app = ValidateApp()
    app.run()