Can Signal Handlers Memory Leak In Pyqt?

Short question: Can signal handlers memory leak. Long question: In C#, if I attach a handler to an event left_object.left_event += right_object.right_handler Then I need to remove

Solution 1:

It is possible to have a memory leak with this design. You need to disconnect the signals and slots if those connections contain references which are keeping objects alive.

Whether or not this actually happens depends on what exactly right_handler is. If right_handler is a closure with a reference to self then you have this problem.

Solution 2:

but in Python I cannot explicitly call the destructor,

You can call destructor in python. Check del and __del__

Do I need to remove the handler to prevent right_objects memory-leaking,

No, you don't need to do that. python will handle that. Run below code check your self.

In this code signal of startButton1 and stopButton1 are connected to methods of class object of Hello and this object(hello1) is attribute of Widget class. So hello1 will live until life object of Widget OR we delete it in method Widget.onDelete with Delete button. Once you click Delete button, destructor of hello1 is called and it will goes out of scope. Now signal of startButton1 and stopButton1 don't work as before.

Now in second row there are buttons startButton2 and stopButton2, whose signal are connected with object of hello2. But as soon as construct of Widget is over hello2 life time is finish. So there is not slot connected for signal of those buttons after Widget construct is over.

from PyQt5.QtWidgets import QApplication,QPushButton,QWidget,QHBoxLayout,QVBoxLayout

classHello():
    def__init__(self):
        print("init")

    defonStart(self):
        print("onStart");

    defonStop(self):
        print("onStop");

    def__del__(self):
        print("del")

classWidget(QWidget):
    def__init__(self,parent=None):
        QWidget.__init__(self,parent);
        vLayout = QVBoxLayout()
        self.setLayout(vLayout)
        buttons1 = QWidget()
        hLayout1 = QHBoxLayout()
        buttons1.setLayout(hLayout1)
        vLayout.addWidget(buttons1)
        startButton1 = QPushButton("Start");
        stopButton1 = QPushButton("Stop");
        deleteButton1 = QPushButton("Delete");
        self.hello1 = Hello();
        startButton1.clicked.connect(self.hello1.onStart)
        stopButton1.clicked.connect(self.hello1.onStop)
        deleteButton1.clicked.connect(self.onDelete)
        hLayout1.addWidget(startButton1);
        hLayout1.addWidget(stopButton1);
        hLayout1.addWidget(deleteButton1);

        buttons2 = QWidget()
        hLayout2 = QHBoxLayout()
        buttons2.setLayout(hLayout2)
        vLayout.addWidget(buttons2)
        startButton2 = QPushButton("Start");
        stopButton2 = QPushButton("Stop");
        deleteButton = QPushButton("Delete");
        hello2 = Hello();
        startButton2.clicked.connect(hello2.onStart)
        stopButton2.clicked.connect(hello2.onStop)
        hLayout2.addWidget(startButton2);
        hLayout2.addWidget(stopButton2);


    defonDelete(self):
        ifhasattr(self,"hello1"):
            del self.hello1

app = QApplication([])
w = Widget();
w.show()
app.exec_()

Hope this will clear you doubt.