Kivy progressbar value won't update

Question

I'm trying to program a progress bar which counts down from 60 to 0 seconds as soon as the screen it is on opens, however I can't work out why the value of the bar isn't updating.

I believed self.ids.pb.value was a valid way to do this, which leads me to think I'm making a mistake elsewhere.

Thanks in advance.

Error

KeyError: 'pb'
AttributeError: 'super' object has no attribute '__getattr__'

.py file

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.button import Button
from kivy.uix.screenmanager import ScreenManager, Screen, CardTransition
from kivy.uix.progressbar import ProgressBar

class CountDown(ProgressBar):

    def count(self):
        self.ids.pb.value = 60
        seconds = 60
        def count_it(seconds):
            if seconds == 0:
                return
            seconds -= 1
            self.ids.pb.value = seconds
            Clock.schedule_once( lambda dt: count_it(seconds), 1)
        Clock.schedule_once( lambda dt: count_it(60), 1)

class EasyMode(Screen):
    pass

class TutorialEasy(Screen):
    pass

class GIFapp(App):
countdown = CountDown()
def build(self):
    return Builder.load_file("testkivy.kv")

Kv file

<TutorialEasy>:
    Button:
        on_release: app.countdown.count()
        on_release: app.root.current = "EasyMode"

<EasyMode>:
    CountDown:
        id: pb
        max:60

Update

Value wasn't updating once errors were fixed because I missed declaring the value in Kv lang ie.

<EasyMode>:
        CountDown:
            id: pb
            max:60
            value: app.countdown.value

Answer 1

The value is already in the CountDown class.
So you can set the value with self.value = seconds

If you are in the EasyMode class, it would work with self.ids.pb.value = seconds