View Extensions

View Extensions are param.Parameterized classes with a view attribute or function. View Extensions are developed almost in the same way as Inheritance Extensions. Their api is different though. You use ViewExtension().view to view a View Extension and InheritanceExtension() to view an Inheritance Extension.

View extensions avoids some of the technical quirks that the Inheritance Extensions comes with at the cost of having to communicate to users they need to append .view to view the extension.


In this example we will develop a Dynamic Number extension that can display a number with the fontsize and green+alpha color ratios depending on the value.

../../_images/dynamic-number.gifDynamic Number Video

We start by importing the dependencies

import panel as pn
import param

Then we implement the View extension.

class DynamicNumber(param.Parameterized):
    """Extension Implementation"""
    value = param.Integer(default=30, bounds=(0,100))
    view = param.ClassSelector(class_=pn.layout.Reactive)

    def __init__(self, **params):
        self.view = pn.pane.HTML()

    @param.depends("value", watch=True)
    def _update_object(self, *events):
        self.view.object = self._get_html(self.value)

    def _get_html(self, value):
        """Main functionality of Extension"""
        font_size = value
        alpha = 1-value/100
        green = int(value*255/100)
        return f"""
    <div style="font-size: {font_size}px;color: rgba(0,{green},0,{alpha}">{value}</div>

Finally we try out the extension

# Create app
extension = DynamicNumber()
app = pn.Column(
# Serve the app

If you compare this example to corresponding HTML Extension example you will notice that

  • Developing the DynamicNumber class has fewer lines and is less quirky.
  • Using the DynamicNumber class uses more lines and is a bit more quirky.

So the question really is. Should you make it easier for the developer or the user of the extension? In the first case you would develop it as a View Extension in the Second as a HTML extension.

If you have an opinion please join the discussions

More Examples

Click the images below to see the code.

../../_images/echarts-gauge-oneway.gifEcharts Gauge Video

Official Panel Examples

The Panel Gallery contains more examples in the section called External libraries.

../../_images/panel-gallery-external-libraries.pngExternal Libraries.