Panel._compute_sizing_mode not gracefully handling None

[banesullivan-kobold]

ALL software version info

(this library, plus any other relevant software, e.g. bokeh, python, notebook, OS, browser, etc)

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  Date: Tue Jan 23 17:55:49 2024 GMT

                OS : Linux
            CPU(s) : 12
           Machine : aarch64
      Architecture : 64bit
               RAM : 23.4 GiB
       Environment : Python

  Python 3.10.13 (main, Oct 12 2023, 02:03:44) [GCC 12.2.0]

             panel : 1.3.7
             bokeh : 3.3.1
             numpy : 1.23.5
             scipy : 1.10.1
           IPython : 8.12.0
        matplotlib : 3.7.1
            scooby : 0.8.0
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Description of expected behavior and the observed behavior

Panel._compute_sizing_mode is not gracefully handling if margin is set as None in the passed props.

Complete, minimal, self-contained example code that reproduces the issue

I am struggling to make a MRE for this as this quirk/bug surfaced after some seemingly innocuous changes to other parts of a larger Panel application I'm working on. I cannot seem to track down exactly why the margin is being set to None with the pn.Row that is causing this.

I'm hoping that adding a check to make sure the margin is not None in this function is easy enough without tracking down the root cause though I also would love to get to the bottom of why the margin in the passed props to this function would ever be None.

Confirmed that self.margin has a value of 0, but that the passed props has margin of None which is preferred here:

panel/panel/layout/base.py

Line 212 in 075b5ae

margin = props.get('margin', self.margin)

Stack traceback and/or browser JavaScript console output

  File "/python/lib/python3.10/site-packages/panel/layout/base.py", line 511, in pop
    self.objects = new_objects
  File "/python/lib/python3.10/site-packages/param/parameterized.py", line 525, in _f
    instance_param.__set__(obj, val)
  File "/python/lib/python3.10/site-packages/param/parameterized.py", line 527, in _f
    return f(self, obj, val)
  File "/python/lib/python3.10/site-packages/param/parameterized.py", line 1545, in __set__
    obj.param._call_watcher(watcher, event)
  File "/python/lib/python3.10/site-packages/param/parameterized.py", line 2486, in _call_watcher
    self_._execute_watcher(watcher, (event,))
  File "/python/lib/python3.10/site-packages/param/parameterized.py", line 2468, in _execute_watcher
    watcher.fn(*args, **kwargs)
  File "/python/lib/python3.10/site-packages/panel/reactive.py", line 374, in _param_change
    self._apply_update(named_events, properties, model, ref)
  File "/python/lib/python3.10/site-packages/panel/reactive.py", line 302, in _apply_update
    self._update_model(events, msg, root, model, doc, comm)
  File "/python/lib/python3.10/site-packages/panel/layout/base.py", line 99, in _update_model
    msg.update(self._compute_sizing_mode(
  File "/python/lib/python3.10/site-packages/panel/layout/base.py", line 241, in _compute_sizing_mode
    width += margin*2
TypeError: unsupported operand type(s) for *: 'NoneType' and 'int'

Screenshots or screencasts of the bug in action

• I may be interested in making a pull request to address this

My current solution is to just monkey patch Panel._compute_sizing_mode with:

from panel.layout.base import Panel

_panel_compute_sizing_mode = Panel._compute_sizing_mode


def _compute_sizing_mode(self, children, props):
    if props.get("margin", self.margin) is None:
        props["margin"] = 0
    return _panel_compute_sizing_mode(self, children, props)


Panel._compute_sizing_mode = _compute_sizing_mode

(in my app, I actually apply the entire function copy/pasted to ensure this is thread safe, but the above is the spirit of it)

[philippjfr]

@banesullivan-kobold Thanks for tracking this down, I'd love to get the fix for this into the 1.3.8 release I'm planning for today. If you get a chance today I'd love to see a PR, but if you're in a time crunch I plan to make a PR myself and then release it.