A simple example of a class you can use for running a background process in PyQt5

thread_pool.py

from PyQt5.QtCore import QObject, QRunnable, QThreadPool, pyqtSignal, pyqtSlot


class WorkerSignals(QObject):
    finished = pyqtSignal()
    result = pyqtSignal(object)
    on_process = pyqtSignal(object)


class Worker(QRunnable):
    def __init__(self, fn, *args, **kwargs):
        super(Worker, self).__init__()
        self.fn = fn
        self.args = args
        self.kwargs = kwargs
        self.signals = WorkerSignals()

    @pyqtSlot()
    def run(self):
        try:
            result = self.fn(*self.args, **self.kwargs)
        except Exception as e:
            result = None
            print(f"Exception in worker thread: {e}")
        self.signals.result.emit(result)
        self.signals.finished.emit()


class ThreadPool:
    def __init__(self):
        self.pool = QThreadPool.globalInstance()

    def start(self, fn, callback=None, on_process=None, *args, **kwargs):
        self.worker = Worker(fn, *args, **kwargs)
        if callback:
            self.worker.signals.result.connect(callback)
        if on_process:
            self.worker.signals.on_process.connect(on_process)
        self.pool.start(self.worker)


if __name__ == '__main__':
    """
    A simple example of using ThreadPool class    
    """
    from PyQt5.QtWidgets import QApplication, QMainWindow, QPushButton, QLabel, QVBoxLayout, QWidget, QProgressBar
    from datetime import datetime
    import time

    app = QApplication([])


    class MainWindow(QMainWindow):
        def __init__(self):
            super().__init__()

            self.button = QPushButton("Start", self)
            self.button.clicked.connect(self.start_thread)
            self.label = QLabel("Waiting...", self)
            self.progress = QProgressBar()
            self.progress.setMaximum(5)

            layout = QVBoxLayout()
            layout.addWidget(self.button)
            layout.addWidget(self.label)
            layout.addWidget(self.progress)

            widget = QWidget()
            widget.setLayout(layout)
            self.setCentralWidget(widget)

            self.thread_pool = ThreadPool()

        def start_thread(self):
            self.button.setEnabled(False)
            self.label.setText("Running...")
            self.thread_pool.start(self.long_running_task, self.task_complete, self.task_on_process)

        def task_on_process(self, result):
            self.progress.setValue(result)

        def long_running_task(self):
            print("Starting long running task...")
            for i in range(6):
                self.thread_pool.worker.signals.on_process.emit(i)
                time.sleep(3)
            print("Long running task complete.")
            return datetime.now().strftime("%Y-%m-%d %H:%M:%S")

        def task_complete(self, result):
            self.label.setText(f"Result: {result}")
            self.button.setEnabled(True)


    window = MainWindow()
    window.show()

    app.exec_()