MNT: Deal with pyside6 throwing an error about __init__ functions in classes with multiple inheritence not getting called, when we actually are calling them.

[nstelter-slac]

There is no issue with this when running on pyqt5, but pyside6 throws a runtime error when initializing classes
that use multiple inheritance of a qt base class and a pydm class.

example class:

class PyDMDrawing(QWidget, PyDMWidget, new_properties=_penRuleProperties))
    ...
    def __init__(self, parent=None, init_channel=None):
         ...
         # explicitly calling base class __init__ functions
	 QWidget.__init__(self, parent)
         PyDMWidget.__init__(self, init_channel=init_channel)
	 ...

The runtime error happens when a call is made in the base class that
relies on the qt base class's __init__ call to have already completed setting
things up (such as 'installEventFilter()).

example error:

    -> self.installEventFilter(self)
    RuntimeError: '__init__' method of object's base class (PyDMDrawingImage) not called.

This error is thrown despite that we explicitly call each of it's base class __init__
functions. It seems like pyside6 is just being extra cautious here.

This is maybe not so great, but to avoid a larger rework of the widget class structures just to appease
this pyside6 error, I propose we just catch this error where it occurs.

[tangkong]

In the case of a pyside6 throwing a RuntimeError, does this prevent the offending methods from being run at all? I wonder why we aren't calling super().__init__ here and letting python do the base-class init wrangling for us. Was that shown not to work before?

[nstelter-slac]

In the case of a pyside6 throwing a RuntimeError, does this prevent the offending methods from being run at all? I wonder why we aren't calling super().__init__ here and letting python do the base-class init wrangling for us. Was that shown not to work before?

hey,

the runtime error ends up killing the whole pydm application.

and im not sure why we opted to not use super() originally, b/c in the case of PyDMDrawing super().__init__(parent, init_channel=init_channel) works great on pyqt5 but still seems to give same error on pyside6.

[nstelter-slac]

looks like it was intentionally changed from super() to individual init calls here:

https://github.com/slaclab/pydm/pull/81/files#diff-131a6cc94441dc20961237f37ed8aa51faa97d5ed485ee68daf8e8766678f658L10

but im not seeing the reasoning why

[tangkong]

Sorry, by "this" I meant more "do the changes in this PR prevent the methods from being run all". My curiosity was more about whether there was some fallback mechanism to trigger the calls that were passed over (e.g. self.installEventFilter(self))

Sorry for being imprecise!

[nstelter-slac]

oh thanks, i had totally confused myself!

i was convinced installEventFilter was getting set up correctly despite catching and passing on the error,
but that doesnt make much sense.

and even if does install the filter before throwing the error, thats not something to rely on.

instead looks like i can just pull those calls out of the base and add it to each child class.

i guess the downside of this is redundancy, and also anyone making new subclasses of PyDMWidget or PyDMPrimitiveWidget has to know they need to makes these calls. (or events wont be filter, etc)

[nstelter-slac]

new idea for addressing this issue is up here: #1181