pyQt4 and inheritance

For a number of reasons I am contemplating redoing an program I use at work in pyqt4 (at present it is in pygtk). After playing around with it and getting a feel for it and appreciating its philosophy with gui building I am running into some annoying ... bugs or implementation limitations

One of them is inheritance:

#!/usr/bin/env python 
#-*- coding: utf-8 -*- 
import sys
from PyQt4 import QtCore, QtGui
app = QtGui.QApplication(sys.argv) 

class A(object): 
    def __init__(self): 
        print "A init" 

class B(A): 
    def __init__(self): 
       super(B,self).__init__() 
       print "B init" 

class C(QtGui.QMainWindow): 
    def __init__(self): 
        super(C,self).__init__()
        print "C init" 

class D(QtGui.QMainWindow,A): 
    def __init__(self): 
        print "D init" 
        super(D,self).__init__() 

print "\nsingle class, no inheritance" 
A() 


print "\nsingle class with inheritance" 
B() 

print "\nsingle class with Qt inheritance" 
C() 


print "\nsingle class with Qt inheritance + one other" 
D()

If I run this I get:

$ python test.py 

single class, no inheritance 
A init 

single class with inheritance 
A init 
B init 

single class with Qt inheritance
C init

single class with Qt inheritance + one other
D init

while I was expecting:

$ python test.py 

single class, no inheritance 
A init 

single class with inheritance 
A init 
B init 

single class with Qt inheritance 
C init 

single class with Qt inheritance + one other 
D init 
A init

Why is it that you cannot use super to initialise the inherited classes when a qt4 class is involved? I would rather not have todo

QtGui.QMainWindow.__init__() 
A.__init__()

Anyone know what is going on?

This is not a QT issue, but a lack of understanding of how multiple inheritance works. You can absolutely use multiple inheritance, but it is a tricky subject in Python.

In a nutshell, in your last example, the first __init__ is called, so if you changed class D(QtGui.QMainWindow,A): to class D(A, QtGui.QMainWindow): you would see A's constructor called, and not QMainWindow's one.

See the following links for further reference on super() behavior with multiple inheritance: