Is there any way to bind a differnt click handler to QPushButton in PyQt5?

Question

I have a QPushbutton:

btn = QPushButton("Click me")
btn.clicked.connect(lambda: print("one"))

Later in my program, I want to rebind its click handler, I tried to achieve this by calling connect again:

btn.clicked.connect(lambda: print("two"))

I expected to see that the console only prints two, but actually it printed both one and two. In other words, I actually bound two click handlers to the button.

How can I rebind the click handler?

Answer 1

Signals and slots in Qt are observer pattern (pub-sub) implementation, many objects can subscribe to same signal and subscribe many times. And they can unsubscribe with disconnect function.

from PyQt5 import QtWidgets, QtCore

if __name__ == "__main__":
    app = QtWidgets.QApplication([])

    def handler1():
        print("one")

    def handler2():
        print("two")

    button = QtWidgets.QPushButton("test")
    button.clicked.connect(handler1)
    button.show()

    def change_handler():
        print("change_handler")
        button.clicked.disconnect(handler1)
        button.clicked.connect(handler2)

    QtCore.QTimer.singleShot(2000, change_handler)

    app.exec()

In case of lambda you can only disconnect all subscribers at once with disconnect() (without arguments), which is fine for button case.