Timers cannot be stopped from another thread - Remove Focus

Question

import sys

from PyQt5.QtCore import QThread
from PyQt5.QtWidgets import QApplication, QWidget, QVBoxLayout, QLineEdit

class Worker(QThread):

    def __init__(self, textBox):
        super().__init__()
        self.textBox = textBox

    def run(self):
        while True:
            if self.textBox.text() == "close":
                app.quit()
                break

            if self.textBox.text() == "removeFocus":
                self.textBox.clearFocus()

class window(QWidget):
    def __init__(self):
        super().__init__()

        vBox = QVBoxLayout()
        self.setLayout(vBox)
        self.resize(600, 400)

        textBox = QLineEdit()
        vBox.addWidget(textBox)

        worker = Worker(textBox)
        worker.start()

        self.show()


if __name__ == "__main__":
    app = QApplication(sys.argv)
    window = window()
    sys.exit(app.exec())

When I type "close" in the textBox it works very fine but when I type "removeFocus", it still works but I get this error:

QObject::killTimer: Timers cannot be stopped from another thread

Why am I getting such an error even though the program is running?

(Since the process I want to do is very simple, I don't think I can go into much detail. I've just started learning Python. This is the first time I use this site. I'm sorry if I made a mistake while creating a post. Thank you)

Answer 1

In Qt you must not access or modify the GUI information from another thread (see this for more information) since it does not guarantee that it works (the GUI elements are not thread-safe), in your case luckily you have no problems but It is dangerous to use your approach in real.

In your case it is also unnecessary to use threads since it is enough to use the textChanged signal from QLineEdit.

import sys

from PyQt5.QtCore import pyqtSlot
from PyQt5.QtWidgets import QApplication, QWidget, QVBoxLayout, QLineEdit


class Window(QWidget):
    def __init__(self):
        super().__init__()

        vBox = QVBoxLayout(self)
        self.resize(600, 400)

        self.textBox = QLineEdit()
        vBox.addWidget(self.textBox)

        self.textBox.textChanged.connect(self.on_text_changed)

    @pyqtSlot(str)
    def on_text_changed(self, text):
        if text == "close":
            QApplication.quit()
        elif text == "removeFocus":
            self.textBox.clearFocus()


if __name__ == "__main__":
    app = QApplication(sys.argv)
    window = Window()
    window.show()
    sys.exit(app.exec())