How to disable button in PyQT5 while another method is running to prevent user to click it and restart the method multiple times? - pyqt5

Question

I would like to know how to disable the button while another method is running by that button, and then re enable it when that method is finished. I tried with the sample code, but that logic does not work, it still clickable and only becomes disabled when the loop finishes in another method. If I click it multiple times during the while loop, then it restart it again and again.
from PyQt5.QtWidgets import QApplication, QMainWindow, QPushButton
import sys
class MainWindow(QMainWindow):
def __init__(self):
super().__init__()
self.setWindowTitle("Demo")
self.button = QPushButton("Press me!")
self.button.clicked.connect(self.the_button_was_clicked)
self.setCentralWidget(self.button)
def the_button_was_clicked(self):
self.button.setText("You already pressed it.")
self.runner()
self.setWindowTitle("Changed title")
def runner(self):
self.button.setEnabled(False)
i = 0
while i < 5000000:
i = i+1
print(i, end=" ")
self.button.setEnabled(True)
app = QApplication(sys.argv)
window = MainWindow()
window.show()
app.exec()

Answer 1

You have 2 problems.
Almost any UI based toolkit uses an event loop, meaning that it has a while-like loop that waits for any event in order to react; as long as you run a blocking function in the same thread of that event loop, it means that that loop is not able to process its events, which will be queued instead and lately processed as soon as control returns to it; among these events there are paint events (those responsible of painting the UI) and input events (those coming from the user interaction); your while loop blocks both of them, meaning that the button will not be displayed as disabled, and all input events will be queued and processed only after the function returns;
the Python buffer (used by print()) is somehow limited, which can block furthermore anything else;
Since Python doesn't allow direct concurrence, you only have two choices: periodically ensure that the event loop process its events (see QCoreApplication.processEvents()), or use multiprocessing capabilities (which can be very tricky if you need UI interaction).
For this simple case, the suggested solution is the former one (including skipping the buffer at all until the string is completed):
def runner(self):
self.button.setEnabled(False)
QApplication.processEvents()
i = 0
print('started')
while i < 5000000:
i = i+1
if not i % 100000:
QApplication.processEvents()
print('finished')
self.button.setEnabled(True)
Remember that processEvents() is possible and tolerated, but you should not use it without awareness: it should only be used when you really know what you are doing and any other alternative is not a viable option. If the processing does not directly deal with CPU-bound aspects (eg. IO management, like file system operation or network retrieval), you should consider threading instead, and always use QThreads and custom signals whenever any result of the processing requires interaction with UI elements, since widgets are NOT thread-safe.