How can I safely communicate data between the main window and a thread in PyQt?

Communicating Data Between Main Window and a Thread in PyQt

In PyQt applications, a common scenario involves sharing data between the main window and a thread while maintaining thread safety. Here are the recommended approaches:

Signals and Slots:

• Declare a custom Qt signal in the thread class, e.g., beep().
• Connect the signal in the main window to a slot that updates the relevant widget, e.g., update().

Example:

<code class="python">class Worker(QtCore.QThread):
    beep = QtCore.pyqtSignal(int)

    def __init__(self, sleep_time):
        super(Worker, self).__init__()
        self.sleep_time = sleep_time

    def run(self):
        i = 0
        while True:
            i += 1
            self.beep.emit(i)
            time.sleep(self.sleep_time)

class MainWindow(QtGui.QWidget):
    def __init__(self):
        # ...
        self.worker = Worker(1)  # Initial sleep time
        self.worker.beep.connect(self.update)
        self.worker.start()

    def update(self, number):
        # Update widget with number
        self.output.display(number)</code>

Caveats:

• Qt widgets are not thread-safe and should only be accessed from the main thread.
• Global variables may not work as expected when accessed from multiple threads.

Other Approaches:

• Passing Host Window Reference: Risky as it relies on QObject thread affinity and can lead to race conditions.
• Keeping Synchronized Copy: Requires maintaining consistency between the main window and the thread, which can be complex.

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