[PyQt] Multiple Inheritance with PyQt5 on python 2

[Baz Walter]

On 09/12/16 12:22, Sebastian Eckweiler wrote:
> Hi there,
>
> I've just read through
> http://pyqt.sourceforge.net/Docs/PyQt5/multiinheritance.html.
> I'm using a self-built PyQt5 for Python 2 on Windows - and it seems I
> can't get multiple inheritance to work:
>
> class SomeClass(object):
>
>     def __init__(self, attr):
>         self.attr = attr
>
> class AnotherDialog(QtWidgets.QDialog, SomeClass):
>
>     def __init__(self, parent=None):
>         #super(AnotherDialog, self).__init__(parent) # tested this was
> well
>         QtWidgets.QDialog.__init__(self, parent)
>         SomeClass.__init__(self, 1)
>
>
> app = QtWidgets.QApplication([])
> dlg = AnotherDialog()
>
> This always results in
>
> TypeError: __init__() takes exactly 2 arguments (1 given)
>
> is there a workaround for this?

The signature of SomeClass has one required positional argument. If you 
use super, how is it going to get that argument if you don't pass it to 
the AnotherDialog constructor?

The docs you linked to explained that you should use keyword arguments. 
So one way to resolve the issue would be like this:

     class SomeClass(object):
         def __init__(self, attr=1, **kwargs):
             super(SomeClass, self).__init__(**kwargs)
             self.attr = attr

     class AnotherDialog(QtWidgets.QDialog, SomeClass):
         def __init__(self, parent=None, **kwargs):
             super(AnotherDialog, self).__init__(parent, **kwargs)

Or, less flexibly, perhaps like this:

     class SomeClass(object):
         def __init__(self, attr):
             super(SomeClass, self).__init__()
             self.attr = attr

     class AnotherDialog(QtWidgets.QDialog, SomeClass):
         def __init__(self, parent=None):
             super(AnotherDialog, self).__init__(parent, attr=1)

Without super, put the mixin first:

     class SomeClass(object):
         def __init__(self, attr):
             self.attr = attr

     class AnotherDialog(SomeClass, QtWidgets.QDialog):
         def __init__(self, parent=None):
             SomeClass.__init__(self, 1)
             QtWidgets.QDialog.__init__(self, parent)