Add param.Bytes mapped to pn.FileInput

[Jhsmit]

I frequently have a set of input parameters in a param.Parameterized class which I expose with pn.Param. Often one of these is a FileInput.
I would like a param.Bytes parameter which maps to a pn.widgets.FileInput by default.

I would like to be able to do:

import param
import panel as pn

class MyApp(param.Parameterized):
    input_file = param.Bytes()

    value_1 = param.Selector(default='a', objects=['a', 'b', 'c'])
    value_2 = param.Integer(3, bounds=(1, 8))

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

        self.markdown = pn.pane.Markdown(object='My markdown',
            width=300)

    @param.depends('input_file', watch=True)
    def _update_mardown(self):
        self.markdown.object = self.input_file.decode()



app = MyApp()
controls = pn.Param(app)
layout = pn.Row(app.markdown, controls)
layout.servable()

Currently I use:

import param
import panel as pn

class MyApp(param.Parameterized):
    input_file = param.Parameter()

    value_1 = param.Selector(default='a', objects=['a', 'b', 'c'])
    value_2 = param.Integer(3, bounds=(1, 8))

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

        self.markdown = pn.pane.Markdown(object='My markdown',
            width=300)

    @param.depends('input_file', watch=True)
    def _update_mardown(self):
        self.markdown.object = self.input_file.decode()



app = MyApp()
controls = pn.Param(app, widgets={'input_file': pn.widgets.FileInput})
layout = pn.Row(app.markdown, controls)
layout.servable()

Desired output:

Which shows the contents of the input file as text in the markdown

[maximlt]

There's an open PR in param that adds a Bytes Parameter (holoviz/param#542) which I guess could be mapped to a FileInput in param.py.