Updating Param.String from TextAreaInput fails in simple Param class

Param
,
1

Hi, I fail to update a Param.String with edited values from the TextAreaInput. My code:

import panel as pn
import param
pn.extension()

class Criterion(param.Parameterized):
    score = param.Integer(3, bounds=(0,5))
    argument_show = param.String(default='not updated')
    argument_edit = param.Parameter
    layout = param.Parameter()
    
    def __init__(self, **params):
        super().__init__(**params)
        self.argument_edit = pn.widgets.input.TextAreaInput(placeholder='Enter argumentation for score', value='test')
        self.layout = pn.Row(self.argument_edit,self.argument_show)
        
    @pn.depends('argument_edit',watch=True)
    def update_argument_show(self):
        self.argument_show = self.argument_edit.value

c = Criterion()
c.layout

image

The reason I want an TextAreaInput rather than the string parameter itself to edit the text value is to enable multiline text.
Any ideas?

2

I think you’re a little bit confused about how parameters work. This line argument_edit = param.Parameter is not a valid parameter definition. So you have two options:

  1. You leave out the parameter definition entirely and point the param.depends call at the value parameter of the widget:
class Criterion(param.Parameterized):
    score = param.Integer(3, bounds=(0,5))
    argument_show = param.String(default='not updated')
    
    def __init__(self, **params):
        self.argument_edit = pn.widgets.input.TextAreaInput(placeholder='Enter argumentation for score', value='test')
        super().__init__(**params)
        self.layout = pn.Row(self.argument_edit, self.param.argument_show)
        
    @pn.depends('argument_edit.value', watch=True)
    def update_argument_show(self):
        self.argument_show = self.argument_edit.value

Also note the change to self.param.argument_show in the layout. If you pass self.argument_show that refers to the current value of the parameter, i.e. it will never update. There is also no need to make layout a parameter.

  1. Alternatively you can make use of the ability to map parameters to arbitrary widgets:

class Criterion(param.Parameterized):
    score = param.Integer(3, bounds=(0,5))
    argument_show = param.String(default='not updated')
    argument_edit = param.String(default='test')
    
    def __init__(self, **params):
        super().__init__(**params)
        self.layout = pn.Row(
            pn.Param(self.param.argument_edit, widgets={'argument_edit': pn.widgets.TextAreaInput}),
            self.param.argument_show
        )

    @pn.depends('argument_edit', watch=True)
    def update_argument_show(self):
        self.argument_show = self.argument_edit
        
c = Criterion()
c.layout