TypeError with PySide 6.5.0 for multiple inheritance of MainWindow

StarterKit

Hi all,
It appears I got a problem after PySide upgrade from 6.4.3 to 6.5.0.
Here is a minimal example - it does nothing special, just displays a window and a label in it. The structure of the code is similar to the one I use in real project where UI is created with help of Qt Designer generated files.
This code works fine with PySide 6.4.3, but with PySide 6.5.0 it raises an error.
The error:

window = MainWindow()
             ^^^^^^^^^^^^^^^^^
File "main.py", line 11, in __init__
  QMainWindow.__init__(self, parent=None)
TypeError: object.__init__() takes exactly one argument (the instance to initialize)

The code:

from PySide6.QtWidgets import QApplication, QMainWindow, QLabel

class Ui_X_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.resize(400, 300)
        self.lbl = QLabel(self)

class MainWindow(QMainWindow, Ui_X_MainWindow):
    def __init__(self):
        QMainWindow.__init__(self, parent=None)
        self.setupUi(self)
        self.lbl.setText("XXX")

app = QApplication([])
window = MainWindow()
window.show()
app.exec()

StarterKit

@JonB said in TypeError with PySide 6.5.0 for multiple inheritance of MainWindow:

For the architecture of this particular logger case. Since you have to derive from logging.Handler, why don't you encapsulate the QPlainTextEdit in your class instead of multiple-inheriting from it? My initial thought is that would be preferable. Then you would not multiple-inherit and you wouldn't have the current problem, whatever it is.

Finally I decided to encaplusate logging.Handler in my class and now I like it more than before :)
The bug was confirmed in PySide and to be corrected in future versions but everything works good without multiple inheritance.

Also initial code was not ideal and was different from Qt recommendations.

So, with both things changed I have my code up and running again.

StarterKit

I downgraded PySide6 to version 6.4.3 (with 2 dependencies - PySide6-Essentials and PySide6-Addons) and it works. So the problem is definitely appeared after an upgrade of PySide to 6.5.0.

JonB

@StarterKit You would need to report this over at https://bugreports.qt.io/.

StarterKit

@JonB unfortunately I don't clearly understand what is wrong here and as a result I feel my bug report will be inconsistent or incomplete...
Do you see something that is obviosly wrong here?... I see that here is some mess with different constructor calls that takes different set of arguments... but I can't make my complain more clear, unfortunately... :(

SGaist

Hi,

I currently don't have a direct answer for this new issue however, the use of super is more common in code designed with Qt for Python. Even more so in Python 3 code bases.

You can see some good reasons here as to why.

StarterKit

@SGaist , while I fully support your point of using super() I can't figure out how to fix this exact error with help of it.

JonB

@StarterKit
If you replace your
QMainWindow.__init__(self, parent=None)
by
super().__init__(self, parent=None) [Should not have self as per @SGaist below.]
does it make the problem go away?

If that does not solve, not that you should have to but try omitting the , parent=None in both the QMainWindow and the super() cases.

SGaist

@JonB said in TypeError with PySide 6.5.0 for multiple inheritance of MainWindow:

@StarterKit
If you replace your
QMainWindow.__init__(self, parent=None)
by
super().__init__(self, parent=None)
does it make the problem go away?

This is wrong, self shall not be part of the arguments passed to the function called when using super.

super().__init__(parent=parent)

JonB

@SGaist Damn, sorry, corrected. I thought I remembered Python :)

StarterKit

@JonB , @SGaist , thanks for your proposal, but probably my message was not clear enough. I tried this code already and it fails with the same error unfortunately :(

  File "main.py", line 10, in __init__
    super().__init__(parent=None)
TypeError: object.__init__() takes exactly one argument (the instance to initialize)

It only works if I put nothing:

super().__init__()

but... in this case I have a failure in another part of my code... (I'm still looking into it but it appears without parent=None some other widget behaves wrong...)

StarterKit

Ok, I found why I my code fails if I use super().__init__().
It happens because I have the same problem in another place... And I don't have a clear idea how to fix it in an easy way.

So, I use python logging module in my app. Traditionally it prints messages to a console by default. You may redirect it to file or something else.

But you may do whatever you want if you create you own handler and pass it to logging.addHandler() method. But your handler should be a descendant of logging.Handler.

So, I use Qt to have GUI and I deciced to put logging output into a Plain text editor.
As result I created a class that is descendant of both - QPlainTextEdit and logging.Handler:

class LogViewer(QPlainTextEdit, logging.Handler):
    def __init__(self, parent=None):
        QPlainTextEdit.__init__(self, parent)
        logging.Handler.__init__(self)
        # Other initialization

    def emit(self, record, **kwargs):
        # log record handling

and then I use it:

self.Logs = LogViewer(parent_widget)
self.logger = logging.getLogger()
self.logger.addHandler(self.Logs)

And as result I have exactly the same prolem TypeError: Level not an integer or a valid string because now it tries to pass parent_widget to logging.Handler constructor.

StarterKit

Should I have

super(QPlainTextEdit, self).__init__(parent)
super(logging.Handler, self).__init__()

instead of:

QPlainTextEdit.__init__(self, parent)
logging.Handler.__init__(self)

?

JonB

@StarterKit

@SGaist said in TypeError with PySide 6.5.0 for multiple inheritance of MainWindow:

This is wrong, self shall not be part of the arguments passed to the function called when using super.
super().init(parent=parent)

That's what he said. I'm not sure enough about my Python to answer, maybe no harm in trying :)

It would be interesting to know if there is a PyQt6.5.0 and how it handles your existing code. You say it was working at 6.4.3, I don't know whether the PySide 6.5 is correct or not.

For the architecture of this particular logger case. Since you have to derive from logging.Handler, why don't you encapsulate the QPlainTextEdit in your class instead of multiple-inheriting from it? My initial thought is that would be preferable. Then you would not multiple-inherit and you wouldn't have the current problem, whatever it is.

StarterKit

@JonB, I've created PYSIDE-2294 where I try to figure out how my code should look like...
The main strange thing indeed is that everything is fine with 6.4.3 and goes to hell with 6.5.0. I'm not a python master but... it worked pretty well before 6.5.0 even if my code isn't ideal :)

With regards to your question about inheritance. I use Qt Designer to create UI layout. So for me it is easier to have Qt-based class that I may use in Qt Designer and simply put an object on form with help of mouse. This is why I inherited from QPlainTextEdit.
I may do it other way around and make another class that would be derived from logging.Handler and then use it as a member of my class. But these two classes will be tightly coupled and won't work one without another.
So... if one way I lose benefits of Qt, another way I have bad design... - and then, why would we have multiple inheritance at all? :) I created this class some time ago and it survived migration from Qt 5 to Qt 6... But now it fails with Qt 6.5.0 :(

StarterKit

Hi all,
So it appears to be a bug introduced in PySide 6.5.0 release that they corrected as result of PYSIDE-2294.

But I try to understand how super() works based on information that I collected.
And I'm a bit puzzled now...
Here is my old code:

import logging
from PySide6.QtWidgets import QApplication, QPlainTextEdit

class LogViewer(QPlainTextEdit, logging.Handler):
    def __init__(self, parent=None):
        QPlainTextEdit.__init__(self, parent)     # this line will be changed
        logging.Handler.__init__(self)            # this line will be changed

app = QApplication([])
window = LogViewer()
window.show()
print(f"LEVEL: {window.level}")
app.exec()

It works and prints LEVEL: 0 as expected.
But based on all these discussions I decided to change it and use super() and got this code:

import logging
from PySide6.QtWidgets import QApplication, QPlainTextEdit

class LogViewer(QPlainTextEdit, logging.Handler):
    def __init__(self, parent=None):
        super().__init__(parent=parent)     # this line was changed

app = QApplication([])
window = LogViewer()
window.show()
print(f"LEVEL: {window.level}")
app.exec()

And this code fails with AttributeError: 'LogViewer' object has no attribute 'level' - it appears that logging.Handler ancestor didn't become a part of window object... I don't understand what is wrong in this case... Any hints?...

I played a bit and changed 2nd example to use different class order: class LogViewer(logging.Handler, QPlainTextEdit) and it gave me TypeError: Handler.__init__() got an unexpected keyword argument 'parent' that raises a feeling that something is not right...

StarterKit

@JonB said in TypeError with PySide 6.5.0 for multiple inheritance of MainWindow:

For the architecture of this particular logger case. Since you have to derive from logging.Handler, why don't you encapsulate the QPlainTextEdit in your class instead of multiple-inheriting from it? My initial thought is that would be preferable. Then you would not multiple-inherit and you wouldn't have the current problem, whatever it is.

Finally I decided to encaplusate logging.Handler in my class and now I like it more than before :)
The bug was confirmed in PySide and to be corrected in future versions but everything works good without multiple inheritance.

Also initial code was not ideal and was different from Qt recommendations.

So, with both things changed I have my code up and running again.

JonB

@StarterKit said in TypeError with PySide 6.5.0 for multiple inheritance of MainWindow:

Finally I decided to encaplusate logging.Handler in my class and now I like it more than before :)

That is indeed the best, but earlier you said

But your handler should be a descendant of logging.Handler.

Anyway, sounds good :)

StarterKit

@JonB said in TypeError with PySide 6.5.0 for multiple inheritance of MainWindow:

That is indeed the best, but earlier you said

I thought one more time about it and decided that there is a better desing option possible :) Not a big change but I moved 2 more methods inside my class and it looks good after all :)

jonton

We have hit this issue too. PySide 6.5.0 appears to use the signature of the last super-class that is initialised for both of them. The example we have is:

    def __init__(self, rootDataModel, parent):
        super(QtCore.QObject, self).__init__(self)
        StateSource.__init__(self, parent, "model")

This results in a runtime error of:

    QtCore.QObject.__init__(self)
TypeError:__init__() missing 2 required positional arguments: 'parent' and 'name'

If I reverse the order of initialisation to:

    def __init__(self, rootDataModel, parent):
        StateSource.__init__(self, parent, "model")
        super(QtCore.QObject, self).__init__(self)

Then the error reports that the StateSource initialiser only should have a single parameter.

jonton

@jonton

This makes me think it's a new bug that has been introduced into the handling of multiple inheritance in PySide.

I don't know enough about the inner workings of PySide, perhaps someone on this forum can shed some light on it?