How to write __init__ method inheriting two classes?

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I have 3 class in my program. Base, Sub_1 and Sub2. Sub_1 inherits from Base and Sub_2 inherits from QThread and Base.

Base class has some pyQtSignal properties which I want other two classes to have. Now I have problem instantiating class Sub_2. When I run this code I get the following error:

QObject::connect: No such signal Sub_2::signal_1()
Traceback (most recent call last):
  File "main.py", line 31, in <module>
    win = MainWindow()
  File "main.py", line 25, in __init__
    self.worker.signal_1.connect(lambda: print('ok 1'))
TypeError: connect() failed between Base.signal_1[] and unislot()

main.py:

from PyQt5.QtWidgets import QMainWindow, QApplication
from PyQt5.QtCore import QObject, pyqtSignal, QThread

class Base(QObject):
    signal_1 = pyqtSignal()
    signal_2 = pyqtSignal()

    def __init__(self):
        super(QObject, self).__init__()


class Sub_1(Base):
    def __init__(self):
        super().__init__()

class Sub_2(QThread, Base):
    def __init__(self):
        super().__init__()


class MainWindow(QMainWindow):
    def __init__(self, *args, **kwargs):
        super(MainWindow, self).__init__(*args, **kwargs)
        self.worker = Sub_2()
        self.worker.signal_1.connect(lambda: print('ok 1'))
        self.worker.signal_2.connect(lambda: print('ok 2'))


import sys
app = QApplication(sys.argv)
win = MainWindow()
win.show()
sys.exit(app.exec_())
pyqt5 python-3.x python
1 Answers

There is no guarantee that QThread.__init__ properly supports multiple inheritance. The call to super().__init__() in Sub2 may therefore not initialize Base as you expect. You can fix this by changing your MRO.

To change the MRO:

class Sub_2(Base, QThread):

You might want to change Base to be more explicit in its support of multiple inheritance. Instead of super(QObject, self).__init__(), write

super().__init__()
user_29887300
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