python class inheritance def __init bit?

Question

I am using Python 3 with PyQt4 and :

I have a first class :

class MainWindow(QtGui.QWidget):

    def __init__(self):
        super(MainWindow, self).__init__()
        self.initUI()

with this function in it :

def Fn_GetSpnBitsValue(self):
        print (self.SpnBits.value())
        self.BitNumber =self.SpnBits.value()
        print(self.BitNumber)
        return self.BitNumber

as you can see I return the value of one of my spinners created in this class Now I want to access this variable "self.BitNumber" from another class. In other language I would very simply write myValue = MainWindow.self.BitNumber but it seems it wont be as easy in python, so I have look at class inheritance so my second class inherit of my first one...

I would be very tempted to write like this ... :

class BitsWindow(QtGui.QWidget, MainWindow):   
    def __init__(self):
        super(BitsWindow, self).__init__()
        self.initUI2()

Which makes perfect sens to me, I tell my second class "look you inherit from this class so everything she know, you know it as well" but I then get this message error :

 class BitsWindow(QtGui.QWidget, MainWindow):
TypeError: Cannot create a consistent method resolution
order (MRO) for bases QWidget, MainWindow

Which don't really make any sens to me actually. By looking further on the web I have think understand the key is in that bit :

def __init__(self):
        super(BitsWindow, self).__init__()
        self.initUI2()

But I really struggle understanding the concept, I am not sure what this is doing despite numerous tutorials and forum answers. (Maybe, probably, didn't find the good ones.)

Any help would be much appreciated;

Many Thanks !

you should mention the python version and the Qt bindings package (PySide, PyQt4, PyQt5). — Schuh
– Schuh, Commented Aug 31, 2014 at 12:08
Apologize that's very true : Python 3 with PyQt4 (adding in the post too). Thanks. — Giant Blob
– Giant Blob, Commented Aug 31, 2014 at 12:29

sebastian · Accepted Answer · 2014-08-31 13:23:51Z

1

The issue is, that BitsWindow inherits from QWidget and MainWindow, even though MainWindow already is a QWidget.

This spoils python's strategy to determine which e.g. which __init__ method it should use, the one of QWidget or the one from MainWindow:

The MainWindow definition tells python to take MainWindow before the ones of QWidget. When you define BitsWindow(QWidget, MainWindow) you give QWidget precedence over MainWindow. These two strategies collide and that's why you get the error.

So, simply change your class definition from

class BitsWindow(QtGui.QWidget, MainWindow):
...

to

class BitsWindow(MainWindow):
...

FWIW, you could also keep the redundant QWidget inheritance if you really want to, if you change the order:

class BitsWindow(MainWindow, QWidget):
    ...

should also work.

EDIT:

Inheritance may however not actually be what you want. You can get that result be simply accessing it from an instance of MainWindow:

main = MainWindow()
myValue = main.Fn_GetSpnBitsValue()

or

main.Fn_GetSpnBitsValue()
myValue = main.BitNumber

edited Aug 31, 2014 at 13:23

answered Aug 31, 2014 at 12:45

sebastian

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3 Comments

Giant Blob Over a year ago

Ha yes of course! Because MainWindow is already inheriting from QtGui.QWidget ! But now my issue is, I get all the layout/buttons...baically a copy past of my whole first class in my second class while I only want to access the result of one function.

Giant Blob Over a year ago

Thanks I see better now. so I simply need to instantiate my class for accessing stuff in it. That makes sens indeed. Just one thing that bother me, the result of my function I am accessing is not the same weither I am printing it directly in the first class or in the second one. Accessing Fn_GetSpnBitsValue() from my second class will always return me the default value of my spinner (1) no matter what value is actually in it.

Giant Blob Over a year ago

Hi, still an issue with your answer actually. main = MainWindow() myValue = main.Fn_GetSpnBitsValue() or main.Fn_GetSpnBitsValue() myValue = main.BitNumber Doing so get myValue in a new instance of my first class rather than getting it from the existing current first class :/

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