Implement PyComponent

[MarcSkovMadsen]

I've been pointing out multiple times that its very hard to create real Panel widgets from the Viewer. Andrew then told me in #7030 that I should be using the CompositeWidget. I had not used that because the Viewer was originally added to enable me and others to create custom Panel components in general, so I thought that was the one I should use.

[codecov]

Codecov Report

Attention: Patch coverage is 96.15385% with 3 lines in your changes missing coverage. Please review.

Project coverage is 81.82%. Comparing base (da68c8a) to head (75c08ea).
Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
panel/custom.py	94.44%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7051      +/-   ##
==========================================
- Coverage   82.23%   81.82%   -0.42%     
==========================================
  Files         334      337       +3     
  Lines       49925    50199     +274     
==========================================
+ Hits        41058    41077      +19     
- Misses       8867     9122     +255     

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[MarcSkovMadsen]

The content here is ready for review.

I believe though that it should be refactored using a new PyComponent class together with the BaseWidget class. The PyComponent should address the missing features of the Viewer and enable to create custom widgets by combining with BaseWidget.

[philippjfr]

-1 on actually documenting CompositeWidget, through composition this can now be achieved using Viewer + WidgetBase.

[philippjfr]

Just read your last comment, glad we agree 😄

[philippjfr]

Just had a look at the tutorial and imo it absolutely does not read like a tutorial. There's no real steps for the user to follow along except for pasting the entire thing into a file and then running it. It's really much closer to a how-to guide.

[MarcSkovMadsen]

Just had a look at the tutorial and imo it absolutely does not read like a tutorial. There's no real steps for the user to follow along except for pasting the entire thing into a file and then running it. It's really much closer to a how-to guide.

Fair point. I will try to improve it. Its just hard for me to see how I can break it further down as it consists of a single class definition and a single function.

[MarcSkovMadsen]

It would like to help finalize this, but its very unclear for me how to proceed.

It seems to me that the PyComponent is in a very preliminary state?

When I run

import panel as pn
import param

from panel.custom import PyComponent


class CounterButton(PyComponent):

    value = param.Integer()

    def __init__(self, **params):
        super().__init__()
        self._layout = pn.widgets.Button(
            name=self._button_name, on_click=self._on_click, **params
        )

    def _on_click(self, event):
        self.value += 1

    @param.depends("value")
    def _button_name(self):
        return f"count is {self.value}"

    def __panel__(self):
        return self._layout

CounterButton(width=300)

I get

TypeError: PyComponent._sync__views() takes 1 positional argument but 2 were given

Do you plan on finalizing the implementation of the PyComponent @philippjfr ? What would the next step be?

[philippjfr]

It seems to me that the PyComponent is in a very preliminary state?

I don't plan on changing anything else, there was just a small typo. I'm unclear whether it's useful or adds anything on top of what Viewer does.

[philippjfr]

Nevermind, it does need a lot more work.

[philippjfr]

The docs can still be improved here but the component now behaves as I'd like it to and I want it to get into an RC release.