Cannot link tap to float slider

[ahuang11]

For widgets, there’s pn.Param and from_param.

What’s the equivalent for HoloViews streams?

https://discourse.holoviz.org/t/whats-the-best-practice-for-linking-up-holoviews-streams-with-parameterized/8215/3

I thought the following would work, but I get TypeError: Constant parameter 'x' cannot be modified

Can we remove the constant=True, or create a dedicated method like from_param or from_params?

import param
import holoviews as hv
import panel as pn
pn.extension()

class TapTest(pn.custom.PyComponent):
    x = param.Number(default=0)
    y = param.Number(default=0)

    def __init__(self, **params):
        super().__init__(**params)

        self._tap = hv.streams.Tap()

        hv_pane = pn.pane.HoloViews()
        hv_pane.object = hv.DynamicMap(self.plot, streams=[self._tap])

        x_spinner = pn.widgets.FloatSlider.from_param(self.param.x)
        y_spinner = pn.widgets.FloatSlider.from_param(self.param.y)
        x_spinner.link(self._tap, value='x', bidirectional=True)
        y_spinner.link(self._tap, value='y', bidirectional=True)
        self._layout = pn.Column(hv_pane, x_spinner, y_spinner)


    def plot(self, x, y):
        return hv.Points([(x, y)]).opts(tools=['tap'])

    def __panel__(self):
        return self._layout

pn.serve(TapTest())

The workaround is a bit more code

import param
import holoviews as hv
import panel as pn
pn.extension()

class TapTest(pn.custom.PyComponent):
    x = param.Number(default=0)
    y = param.Number(default=0)

    def __init__(self, **params):
        super().__init__(**params)

        self._tap = hv.streams.Tap()
        hv_pane = pn.pane.HoloViews()
        hv_pane.object = hv.DynamicMap(self.plot, streams=[self._tap])
        
        pn.bind(self.update_tap, self.param.x, self.param.y, watch=True)
        
        self._layout = pn.Column(hv_pane, self.param.x, self.param.y)

    def update_tap(self, x, y):
        self._tap.event(x=x, y=y)

    def plot(self, x, y):
        if x and y:
            self.param.update(x=x, y=y)
        return hv.Points([(self.x, self.y)]).opts(tools=['tap'])

    def __panel__(self):
        return self._layout

pn.serve(TapTest())

[philippjfr]

This issue has been mentioned on HoloViz Discourse. There might be relevant details there:

https://discourse.holoviz.org/t/whats-the-best-practice-for-linking-up-holoviews-streams-with-parameterized/8215/4

[philippjfr]

Fully in favor.

[ahuang11]

Not sure how to link the params:

import param
import holoviews as hv
import panel as pn

pn.extension()

class Test(pn.custom.PyComponent):

    x = param.Number(default=1, allow_refs=True)
    y = param.Number(default=0.5, allow_refs=True)

    def __init__(self, **params):
        super().__init__(**params)

        self._tap = hv.streams.Tap.from_param(x=self.param.x, y=self.param.y)
        hv_pane = pn.pane.HoloViews(object=hv.DynamicMap(self.plot, streams=[self._tap]))
        self._layout = pn.Column(hv_pane, self.param.x, self.param.y)

    def plot(self, x, y):
        return hv.Points([(x, y)]).opts(tools=['tap'], xlim=(0, 2), ylim=(0, 2))


    def __panel__(self):
        return self._layout

test = Test()
test

Under the hood changes:

class Tap(PointerXY):
    """
    The x/y-position of a tap or click in data coordinates.
    """
    x = param.ClassSelector(class_=pointer_types, default=None,
                            constant=False, allow_refs=True, doc="""
           Pointer position along the x-axis in data coordinates""")

    y = param.ClassSelector(class_=pointer_types, default=None,
                            constant=False, allow_refs=True, doc="""
           Pointer position along the y-axis in data coordinates""")

    @classmethod
    def from_param(cls, x=None, y=None):
        tap = cls(x=x, y=y)
        tap._x_parameterized = x.owner if isinstance(x, param.Parameter) else None
        tap._y_parameterized = y.owner if isinstance(y, param.Parameter) else None
        tap.param.watch(tap._event, ["x", "y"])
        return tap

    def _event(self, *events):
        print(self.x, self.y)
        self._x_parameterized.x = self.param.x
        self._y_parameterized.y = self.param.y
        self.trigger([self])

It works fine, until tapping... then it unsyncs the widget when tapped.

Screen.Recording.2024-10-09.at.2.49.04.PM.mov