pn.bind does not support the watch argument

[MarcSkovMadsen]

I was just trying out pn.bind and I can see that it does not support setting watch=True. This limits the use cases. Then it's just easier to stick with @pn.depends as it supports all use cases.

In the below example the slider does not work.

import numpy as np
import panel as pn
import pandas as pd
import plotly.graph_objects as go

pn.extension('plotly')

data = {}
for i in range(10):
    xo = 5 * np.random.rand()
    xf = 5 + 5 * np.random.rand()
    x = np.linspace(xo, xf, int(50 + 50*np.random.rand()))
    e = np.random.rand()
    y = x**(1+e) * np.cos(x) + 4*(np.random.rand(len(x)) - 0.5)
    data[i] = {
        'x': x.tolist(),
        'y': y.tolist()
    }

nlines = pn.widgets.IntSlider(name='Number of lines', value=2, start=1, end=9)
timeseries = pn.pane.Plotly()

def get_plot(nlines):
    print("get_plot", nlines)
    fig = go.Figure()
    for i in range(nlines):
        fig.add_trace(
            go.Scatter(x=data[i]['x'], y=data[i]['y'], mode='lines', name=f'line-{i}'))
    timeseries.object = fig
get_plot(nlines.value)
pn.bind(get_plot, nlines=nlines, watch=True)

pn.Row(nlines, timeseries).servable()

[jbednar]

Here I assume you meant pn.bind(get_plot, nlines=nlines, watch=True)? That's an interesting suggestion, addressing something @jlstevens was worried about, i.e. that pn.bind only generates updates when the output of it is embedded in a Panel layout. I guess with watch=True that semantics would change, and it would be registered for updates regardless of whether it's in a layout?

[MarcSkovMadsen]

Exactly

[jlstevens]

This was indeed something that bothered me about bind.

Like Marc, I would like the option to watch it (can be off by default) but the problem I have with watch=True is that it means there is a namespace clash with any potential parameter called watch. I guess an actual watch parameter would take precedence (in which case you wouldn't be able to watch it?!).

[jbednar]

I think bind's own watch argument should take precedence, because if it ever clashes, you can always just wrap whatever function you want in a lambda that renames the original function's watch argument. Seems cleaner for bind to strip off things it knows about, consume them, and pass all the rest down to the function, without having to inspect the underlying function for clashes.

[MarcSkovMadsen]

Agree that watch is special and reserved for Param/ Panel.

This PR adds the support #2000

[jlstevens]

I suppose a lambda would be an annoying (but valid) solution and I agree that it is probably best to consume watch as an instruction to bind first. I generally dislike these kinds of namespace clashes but in this case I value being able to watch things more.

I would mention @MarcSkovMadsen that bind is being added to param right now and it is important that things match up before any releases happen: holoviz/param#460