Spinner widget doesn't honor bounds when created from Param object

[sdc50]

The Spinner widget allows you to set a start and end bound. The widget does not let a user set the number outside the bounds:

pn.widgets.Spinner(start=0, end=5)

When creating a Spinner widget from a param.Number I would have expected the start and end to be derived from the bounds of the param object.

class Demo(param.Parameterized):
    a = param.Number(default=5, bounds=(0, 5))
    
    
    def panel(self):
        return pn.widgets.Spinner.from_param(self.param.a)

However, in this case if a user tries to specify a number outside of the bounds the widget allows it and then it raises an error:

Traceback (most recent call last):
  File "~/miniconda/envs/myenv/lib/python3.7/site-packages/pyviz_comms/__init__.py", line 325, in _handle_msg
    self._on_msg(msg)
  File "~/miniconda/envs/myenv/lib/python3.7/site-packages/panel/viewable.py", line 273, in _on_msg
    doc.unhold()
  File "~/miniconda/envs/myenv/lib/python3.7/site-packages/bokeh/document/document.py", line 669, in unhold
    self._trigger_on_change(event)
  File "~/miniconda/envs/myenv/lib/python3.7/site-packages/bokeh/document/document.py", line 1180, in _trigger_on_change
    self._with_self_as_curdoc(event.callback_invoker)
  File "~/miniconda/envs/myenv/lib/python3.7/site-packages/bokeh/document/document.py", line 1198, in _with_self_as_curdoc
    return f()
  File "~/miniconda/envs/myenv/lib/python3.7/site-packages/bokeh/util/callback_manager.py", line 161, in invoke
    callback(attr, old, new)
  File "~/miniconda/envs/myenv/lib/python3.7/site-packages/panel/reactive.py", line 301, in _comm_change
    self._process_events({attr: new})
  File "~/miniconda/envs/myenv/lib/python3.7/site-packages/panel/reactive.py", line 262, in _process_events
    self.param.set_param(**self_events)
  File "~/miniconda/envs/myenv/lib/python3.7/site-packages/param/parameterized.py", line 1526, in set_param
    self_._batch_call_watchers()
  File "~/miniconda/envs/myenv/lib/python3.7/site-packages/param/parameterized.py", line 1665, in _batch_call_watchers
    self_._execute_watcher(watcher, events)
  File "~/miniconda/envs/myenv/lib/python3.7/site-packages/param/parameterized.py", line 1627, in _execute_watcher
    watcher.fn(*args, **kwargs)
  File "~/miniconda/envs/myenv/lib/python3.7/site-packages/panel/param.py", line 438, in link_widget
    self.object.param.set_param(**{p_name: change.new})
  File "~/miniconda/envs/myenv/lib/python3.7/site-packages/param/parameterized.py", line 1519, in set_param
    setattr(self_or_cls, k, v)
  File "~/miniconda/envs/myenv/lib/python3.7/site-packages/param/parameterized.py", line 316, in _f
    instance_param.__set__(obj, val)
  File "~/miniconda/envs/myenv/lib/python3.7/site-packages/param/parameterized.py", line 318, in _f
    return f(self, obj, val)
  File "~/miniconda/envs/myenv/lib/python3.7/site-packages/param/__init__.py", line 624, in __set__
    super(Dynamic,self).__set__(obj,val)
  File "~/miniconda/envs/myenv/lib/python3.7/site-packages/param/parameterized.py", line 318, in _f
    return f(self, obj, val)
  File "~/miniconda/envs/myenv/lib/python3.7/site-packages/param/parameterized.py", line 940, in __set__
    self._validate(val)
  File "~/miniconda/envs/myenv/lib/python3.7/site-packages/param/__init__.py", line 908, in _validate
    self._validate_bounds(val, self.bounds, self.inclusive_bounds)
  File "~/miniconda/envs/myenv/lib/python3.7/site-packages/param/__init__.py", line 872, in _validate_bounds
    "not %s." % (self.name, vmax, val))
ValueError: Parameter 'a' must be at most 5, not 6.

Even if you manually set the start and end values in the from_param call you get the same error:

class Demo(param.Parameterized):
    a = param.Number(default=5, bounds=(0, 5))
    
    
    def panel(self):
        return pn.widgets.Spinner.from_param(self.param.a, start=self.param.a.bounds[0], end=self.param.a.bounds[1])

It seems like the start and end values are being passed through:

But if you set start and end after the widget is created then it works as expected:

[sdc50]

This probably goes without saying, but I would expect the Spinner object to honor the softbounds if it is specified, otherwise it should honor the bounds.

[jbednar]

When creating a Spinner widget from a param.Number I would have expected the start and end to be derived from the bounds of the param object.

I agree; that sounds like a bug!

This probably goes without saying, but I would expect the Spinner object to honor the softbounds if it is specified, otherwise it should honor the bounds.

Softbounds were designed for a slider widget where some bounds are required before displaying anything. For a spinner widget, I would expect softbounds to be ignored; they are only hints, and if the user wants the value to go outside the soft bounds, why not let them?

[maximlt]

As a workaround you could use pn.widgets.IntInput.from_param(...) instead of pn.widgets.Spinner.