What is the correct method of handling events in PyQt 4?

Question

I have seen examples like this:

self.connect(self.ui.add_button, QtCore.SIGNAL('clicked()'),self.printer)

And examples like this:

self.ui.add_button.clicked.connect(self.printer)

I'm just starting to learn Qt; which one should I focus on?

Answer 1

I think that the second example is only supported by some Qt versions (the newer ones), while the first it supported by older ones. But, both are correct.

Answer 2

AFAIK, the newer style doesn't work if there are overloaded signals, so

self.ui.add_button.clicked.connect(self.printer)

can't be used if there's also, say, a

clicked(float, float)

so you'd have to fall back to the older style. It's always good to know both.

Answer 3

I know this post is pretty old, but I just stumbled across it, maybe you will too and now this saves your day ;) ok... by the way, it's my first post here on SO, yey!

WARNING, i did not test this code, i just copied some snippets of code i wrote some time ago, so, there may be some error, but I hope it helps anyway

PyQt's new style signals briefly:

# notice that the signal declarations are at class level (not inside some method)

class MyClass(QObject):    # must subclass QObject (or subclass)

    # declaring signals
    mySimpleSignal = pyqtSignal()
    mySignalWithArguments = pyqtSignal(int, list)
    myOverloadedSignal = ([int, object],[str,object])

    def __init__(self, parent=None):
        super(MyClass,self).__init__(parent=parent)    # remember to init the super class
        [...]

    # methods
    [...]

    # connecting signals
    def connectSignalsMethod(self):
        # connecting simple signal
        self.mySimpleSignal.connect(self.mySlot)
        # connecting signal with arguments
        self.mySignalWithArguments.connect(self.mySlotWithArguments)
        # connecting overloaded signals
        self.myOverloadedSignal[int, object].connect(self.mySlot1)
        self.myOverloadedSignal[str, object].connect(self.mySLot2)

        # same syntax for disconnect()


    # emitting signals
    def emitSignalsMethod(self):
        # emitting simple signal
        self.mySimpleSignal.emit()
        # emitting signal with arguments
        self.mySignalWithArguments.emit(123,['this','is','a','list'])
        # emitting overloaded signal
        myOverloadedSignal[str,object].emit('this is a string', myObject)


    # my slots
    @pyqtSlot()
    def mySlot(self):
        print('hey!')

    @pyqtSlot(int, list)
    def mySlotWithArguments(self, someNumber, someList):
        print('got a number: %d and a list: %s' % (someNumber, someList))

    @pyqtSlot(int, object)
    def mySlot1(self, intArg, objectArg):
        print('got an int and an object')

    @pyqtSlot(str, object)
    def mySlot2(self, str, object):
        print('got a string and an object')

    # an overloaded slot
    @pyqtSignal(int)
    @pyqtSignal(str)
    def overloadedSlot(someArgument)
        print('got something: %s' % someArgument)

otherwise, try this http://www.harshj.com/2010/05/06/pyqt-faq-custom-signals-jpeg-mouse-hovers-and-more/#custom

Edit: events and signals are not the same, what you see above is about signals