Update LCD Number countdown

Question

I'm very new to Python and I have made a very simple countdown timer. The GUI was created in Qt Designer. There is a spin box for input of seconds, a start button and an LCD number counter. The counter counts down fine using the code below:

     def start_btn_clicked(self):
         x = self.Minute_spinBox.value()
         for i in xrange(x,0,-1):
             time.sleep(1)
             print (i)

So that I could see what was happening as I played around with it, I added the print instruction so that it shows the countdown in the Python console as it runs. I then thought I could maybe quite easily have the LCD number display the countdown with something like:

    self.lcdNumber.display(i)("%SS")

But no matter what I try, I cant get it to show. With the line above, I get the first number displayed, but then I get an error saying:

    self.lcdNumber.display(i)("%SS")
    TypeError: 'NoneType' object is not callable

I have tried so many variations that I no longer know where I started and here was me thinking it would be simple. I'd love to know why I cant get it to display the countdown.

Solution

The display function returns None, so doing None("%SS") obviously isn't allowed.

self.lcdNumber.display(i) is enough to show the countdown!

---

To let Qt paint the widgets while looping run the countdown from another thread. See an example.

import time
from threading import Thread
from PyQt4.QtGui import QApplication, QMainWindow, QLCDNumber

class Window(QMainWindow):

    def __init__(self):
        QMainWindow.__init__(self)
        self.lcdnumber = QLCDNumber(self)
        self.resize(400, 400)

        t = Thread(target=self._countdown)
        t.start()

    def _countdown(self):
         x = 10
         for i in xrange(x,0,-1):
             time.sleep(1)
             self.lcdnumber.display(i)

if __name__ == "__main__":
    app = QApplication([])
    window = Window()
    window.show()
    app.exec_()