Error “QObject::startTimer: QTimer can only be used with threads started with QThread” many times when closing application

I know this has been asked many times before. I read all of those threads, and my case seems different. Everybody else who has this trouble has a few straightforward causes that I think I’ve ruled out, such as:

• Starting a timer with no event loop running
• Starting/stopping a timer from a thread other than the one that created the timer
• Failing to set the parent property of a widget, leading to problems with the order of destruction

Below I have a minimal code sample that demonstrates the problem. Notice that I’ve started no threads or timers. I also have set the parent of every widget. If I remove the graph widgets, the problem goes away, so one is tempted to blame pyQtGraph, however, if I include the plot widgets but exclude all the blank tabs (i.e. every tab except tabCatchaTiger), the problem also goes away, and that seems to vindicate pyQtGraph.

Versions:

• Windows 7
• Python 2.7.8
• Wing IDE 5.0.9-1
• PyQt 4.11.1
• PyQwt 5.2.1
• PyQtGraph 0.9.8

Test case:

from PyQt4 import Qt, QtGui, QtCore
import PyQt4.Qwt5 as Qwt
import pyqtgraph as pg

pg.functions.USE_WEAVE = False # Lets pyqtgraph plot without gcc

pg.setConfigOption('background', 'w')
pg.setConfigOption('foreground', 'k')

# GUI for visualizing data from database
class crashyGUI(QtGui.QWidget) :

    def __init__(self) :
        # Make the window
        QtGui.QWidget.__init__(self)
        self.resize(700, QtGui.QDesktopWidget().screenGeometry(self).height()*.85)
        self.setWindowTitle('Data Visualization')

        # Create tab interface
        tabWidget = QtGui.QTabWidget(self)

        # define the tab objects
        self.tabEeny = QtGui.QWidget(tabWidget)
        self.tabMeeny = QtGui.QWidget(tabWidget)
        self.tabMiney = QtGui.QWidget(tabWidget)
        self.tabMoe = QtGui.QWidget(tabWidget)
        self.tabCatchaTiger = QtGui.QWidget(tabWidget)
        self.tabByThe = QtGui.QWidget(tabWidget)
        self.tabToe = QtGui.QWidget(tabWidget)

        # Initialize the tab objects
        self.initTabCatchaTiger()

        ###########################################
        ############### Main Layout ###############
        ###########################################

        tabWidget.addTab(self.tabEeny, 'Eeny')
        tabWidget.addTab(self.tabMeeny, 'Meeny')
        tabWidget.addTab(self.tabMiney, 'Miney')
        tabWidget.addTab(self.tabMoe, 'Moe')
        tabWidget.addTab(self.tabCatchaTiger, 'Catch a Tiger')
        tabWidget.addTab(self.tabByThe, 'By The')
        tabWidget.addTab(self.tabToe, 'Toe')

        self.mainLayout = QtGui.QVBoxLayout(self)
        self.mainLayout.addWidget(tabWidget)

        self.setLayout(self.mainLayout)

    def initTabCatchaTiger(self):
        ###########################################
        ############# ADC Capture Tab #############
        ###########################################
        # define tab layout
        grid = QtGui.QGridLayout(self.tabCatchaTiger)

        # create copy of adc plot and add to row 3 of the grid
        self.catchaTigerPlot1 = pg.PlotWidget(name = 'Catch a Tiger 1', parent = self.tabCatchaTiger)
        self.catchaTigerPlot1.setTitle('Catch a Tiger 1')
        grid.addWidget(self.catchaTigerPlot1, 2, 0, 1, 8)

        self.catchaTigerPlot2 = pg.PlotWidget(name = 'Catch a Tiger 2', parent = self.tabCatchaTiger)
        self.catchaTigerPlot2.setTitle('Catch a Tiger 2')
        grid.addWidget(self.catchaTigerPlot2, 3, 0, 1, 8)

        # set layout for tab
        self.tabCatchaTiger.setLayout(grid)

    def closeEvent(self, event) :
            pass

def main() :
    # open a QApplication and dialog() GUI
    app = QtGui.QApplication([])

    windowCrashy = crashyGUI()
    windowCrashy.show()
    app.exec_()

main()

Answer

Personally, I don’t put any effort into chasing exit crashes anymore–just use pg.exit() and be done with it.

(but if you do happen to find a bug in pyqtgraph, don’t hesitate to open an issue on github)