Don't set class attributes during initialization and don't warn when setting non-Param class attributes

[maximlt]

Fixes #174

• Setting a non-Parameter class attribute no longer raises a warning
• Setting a non-Parameter in the constructor raises a TypeError (breaking change)

[maximlt]

Oh wait, need to resolve conflicts...

[Hoxbro]

Is TypeError the best type of error to raise? Maybe AttributeError? I could be wrong, though, or there could be an even better error.

[maximlt]

TypeError is the error raised by Python when you pass a non expected keyword argument in a function call. That's why I chose it.

Do you have suggestions for a better error?

[Hoxbro]

Maybe a custom one? That sets it apart from normal Python behavior? ParametrizedError

[maximlt]

It seems to be this is a general Python behavior, you shouldn't be able to pass kwargs to a callable that don't expect them. I don't really see a reason to raise a different error here. One could actually argue that Param should raise the exact same error message.

[Hoxbro]

One could actually argue that Param should raise the exact same error message.

I agree.

[maximlt]

The error message now mirrors Python more closely.

Pure Python:

Param on this branch:

[Hoxbro]

I like it. I just ran this PR across the holoviz ecosystem and got two failing tests related to this change:

FAILED panel/tests/pane/test_holoviews.py::test_holoviews_with_widgets_not_shown - TypeError: HoloViews.__init__() got an unexpected keyword argument 'show_widgets'
---
FAILED hvplot/tests/testinteractive.py::test_interactive_pandas_frame_bind_operator_out_widgets - TypeError: Select.__init__() got an unexpected keyword argument 'default'

This does not necessarily mean these changes are wrong, but some tests need to be updated.

[jbednar]

I think this is the correct change, thanks!

[maximlt]

Great thanks! Merging.