Expressify shiny widgets

[gshotwell]

I mostly included the apps from the new ipywidget docs. One bit that might need a callout is the render.express example. I wanted something which returned a context manager, and iterator, and a rendering function, and to do that I needed to be explicit aobut the output. This is basically a module workaround, but I think it's a pretty good example of what render.expresscan do.

from shiny import render
from shiny.express import ui, input, output
import numpy as np
import matplotlib.pyplot as plt


ui.input_slider("n", "Number of cards", value=3, min=1, max=5)


@render.express
def cards():
    with ui.layout_columns():
        for i in range(input.n()):
            with ui.card():
                f"Card {i}"

                @output(id=f"hist_{i}")
                @render.plot(alt="A histogram")
                def histogram():
                    np.random.seed(19680801)
                    x = 100 + 15 * np.random.randn(437)
                    plt.hist(x, 20, density=True)