Main thread - worker thread communication.

[wysota]

Are you sure this is correct?

class WorkerThread(QtCore.QThread):
    def __init__(self, start, end):
        QtCore.QThread.__init__(self)
        self.start = start
        self.end = end

class WorkerThread(QtCore.QThread):
    def __init__(self, start, end):
        QtCore.QThread.__init__(self)
        self.start = start
        self.end = end

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You have a variable called start and then you call start as a method. Try using a different name here. Maybe that's the problem.