Question

I am looking for a way to setup a number of timed function calls in pyqt, with a way to cancel all pending calls when needed.

I was looking at using QtCore.QTimer to setup the function calls, but I don’t know of any good way to cancel these calls. Any ideas?

I can’t seem to find any way to cancel after using QtCore.QTimer.singleShot(1000, self.function). If instead I create a list of QTimer objects I can stop them, but then I am forced to manage a list of timer objects (creation, deletion, which are active, etc.), which I would like to avoid.

# Setup a timer object.
timer = QtCore.QTimer(self)
timer.timeout.connect(self.function)
timer.setSingleShot(True)
timer.start(1000)

# To stop the timer object at some later point.
timer.stop()

I could also manage my own queue of pending function calls, which I would also like to avoid if possible (for the sake of simplicity).

Here is some dummy code showing the kind of thing I am trying to do:

import sys
from PyQt4 import QtCore

class Test(QtCore.QObject):

    def __init__(self, parent=None):
        QtCore.QObject.__init__(self, parent)
        

    def addDelayedCall(self, time, function):
        # Do something here.
        pass


    def clearPendingCalls(self):
        print('  Clearing pending function calls.')
        # Do something here.


    def setupCalls(self):
        self.addDelayedCall(500, self.dummy)
        self.addDelayedCall(1000, self.dummy)
        self.addDelayedCall(1500, self.dummy)
        self.addDelayedCall(2000, self.dummy)


    def dummy(self):
        print('dummy just got called.')


if __name__ == '__main__':
    app = QtCore.QCoreApplication(sys.argv)
    test = Test(app)

    QtCore.QTimer.singleShot(0, test.setupCalls)
    QtCore.QTimer.singleShot(1250, test.clearPendingCalls)
                   
    QtCore.QTimer.singleShot(5000, app.quit)            
    sys.exit(app.exec_())

Answer 1

I have come up with a solution by directly using the timer functionality provided by QObject. I suspect that there is a more elegant solution, but this will probably work for what I need.

import sys
from PyQt4 import QtCore


class Test(QtCore.QObject):

    def __init__(self, parent=None):
        QtCore.QObject.__init__(self, parent)

        self.timers = {}


    def timerEvent(self, event):
        function = self.timers.pop(event.timerId())
        self.killTimer(event.timerId())
        function()


    def addDelayedCall(self, time, function):
        timer_id = self.startTimer(time)

        self.timers[timer_id] = function


    def clearPendingCalls(self):
        print('  Clearing pending function calls.')

        while self.timers:
            timer_id, function = self.timers.popitem()
            self.killTimer(timer_id)


    def setupCalls(self):
        self.addDelayedCall(500, self.dummy)
        self.addDelayedCall(1000, self.dummy)
        self.addDelayedCall(1500, self.dummy)
        self.addDelayedCall(2000, self.dummy)


    def dummy(self):
        print('dummy just got called.')




if __name__ == '__main__':
    app = QtCore.QCoreApplication(sys.argv)
    test = Test(app)

    QtCore.QTimer.singleShot(0, test.setupCalls)
    QtCore.QTimer.singleShot(1250, test.clearPendingCalls)

    QtCore.QTimer.singleShot(5000, app.quit)            
    sys.exit(app.exec_())