PyQt5: Update labels inrun time

Question

I have a problem updating labels in a loop during run time. I think I need to use signals and so on, but I've tried everything I can think of now. What I want my program to do:

When I click the button a loop should start that run some function that take some time. While the function is running the corresponding label should update its text to say "running" and when its done it should say "done" and continue to the next function. I've created some dummy code that represent what I'm after!

I have represented my function with a dummy function that just take some time.

import sys
from PyQt5.QtWidgets import *
import time

class Example(QWidget):

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

        self.initUI()


    def initUI(self):
        # Set up an example ui
        qbtn = QPushButton('Click', self)
        qbtn.clicked.connect(self.changeLabels)
        qbtn.resize(qbtn.sizeHint())
        qbtn.move(100, 50)
        # Add labels
        self.labels = list()
        self.labels.append(QLabel("Lbl1", self))
        self.labels[-1].setFixedSize(50, 20)
        self.labels.append(QLabel("Lbl2", self))
        self.labels[-1].setFixedSize(50, 20)
        self.labels[-1].move(0, 20)
        self.labels.append(QLabel("Lbl3", self))
        self.labels[-1].setFixedSize(50, 20)
        self.labels[-1].move(0, 40)

        self.setGeometry(300, 300, 250, 150)
        self.setWindowTitle('Test')
        self.show()

    def changeLabels(self):
        # Loop over all labels. For each label a function will be executed that will take some time. In this case
        # I represent that with a dummy function to just take time. While the function is running the label should say
        # "running" and when its finished it should say "done".
        for lbl in self.labels:
            orgTxt = lbl.text()
            lbl.setText("%s Running" % orgTxt)
            self.dummyFunction()
            lbl.setText("%s Done" % orgTxt)

    def dummyFunction(self):
        time.sleep(1)


if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())

You need to run your function in another thread and update text via signal/slot. — Dmitry Sazonov, Jan 24 '18 at 08:34

score 1 · Accepted Answer · answered Jan 24 '18 at 12:16

The GUI does not support blocking tasks because the GUI needs some time to update some attributes of the window, a possible solution is to use a new thread and implement the dummy function, in the following example the implementation is shown with the use of signals. If your real function updates any GUI view you should not do it directly in the thread, you should do it through signals.

class DummyThread(QThread):
    finished = pyqtSignal()
    def run(self):
        time.sleep(1)
        self.finished.emit()

class Example(QWidget):
    [...]
    def changeLabels(self):
        for lbl in self.labels:
            orgTxt = lbl.text()
            lbl.setText("%s Running" % orgTxt)
            thread = DummyThread(self)
            thread.start()
            thread.finished.connect(lambda txt=orgTxt, lbl=lbl : lbl.setText("%s Done" % txt))

score 1 · Answer 2 · answered Jan 27 '18 at 16:16

An easier way would be to call QApplication.processEvents() to force QT to process all the events present on the queue. But the UI won't be as responsive as it would be with another thread doing the work and sending signals to the main thread as stated in other answers.

PyQt5: Update labels inrun time

2 Answers2

Linked