import sys
import time
from itertools import count
from PyQt5 import QtCore, QtWidgets


class Worker(QtCore.QThread):
    data_ready = QtCore.pyqtSignal(str)

    def __init__(self):
        super().__init__()

    def run(self):
        time.sleep(5)
        for i in count(1):
            self.data_ready.emit(f"Iteration number {i}")
            time.sleep(1)


if __name__ == '__main__':
    app = QtWidgets.QApplication(sys.argv)
    label = QtWidgets.QLabel("Waiting data...")
    work = Worker()
    work.data_ready.connect(label.setText)
    work.start()
    label.show()
    sys.exit(app.exec_())