Can't set .text to label with id in BoxLayout from .kv file on VSCode

I'm developing an android app which shows schedule. I followed some tutorials and eventually made these pieces of code:

ui.py

import kivy
from kivy.app import App
from kivy.uix.boxlayout import BoxLayout

from kivy.lang import Builder

kivy.require('1.9.0')

class schedule(BoxLayout):
    def __init__(self):
        super(schedule, self).__init__()
    def showSchedule(self):
        self.scheduleText.text = str("12345")

class appFrontEnd(App) :
    def build(self):
        return schedule()
    
Builder.load_file("frontend.kv")
frontEnd = appFrontEnd()
frontEnd.run()

frontend.kv

<schedule>:
    scheduleText: scheduleText
    BoxLayout:
        orientation:'vertical'

        Label:
            text: "Schedule"
            font_size: 64
            color: 0.92, 0.45, 0
        Label:
            id: scheduleText
            text: "No"
            font_size: 21
        Button:
            text: "Update schedule"
            font_size: 32
            size: 100, 50

Code runs with no errors and I can see and interact with the button, but text with id scheduleText is still printing "No".

I have tried Builder.load_string to access this text, but no luck there. Wanted to ask how to fix this problem?

Solution

Button doesn't know that it has to run code - because you forgot on_press: ...

    Button:
        text: "Update schedule"
        font_size: 32
        size: 100, 50
        on_press: root.showSchedule()

That's all.

Full code (with smaller modifications):

main.py

import kivy
from kivy.app import App
from kivy.uix.boxlayout import BoxLayout


class Scheduler(BoxLayout):  # PEP8: `CamelCaseNames` for classes 

                             # no need `__init__`
    
    #def show_schedule(self):  # PEP8: `lower_case_names` for functions
    #    print("clicked")      # for tests - to check if Button even executes it
    #    self.schedule_text.text = "12345"  # no need `str()`

    def show_schedule(self, widget):  # with access to clicked button
        print("clicked:", widget.text)
        self.schedule_text.text = "12345"

class FrontEndApp(App):   # `FronEndApp` loads automatically `frontend.kv`
    def build(self):
        return Scheduler()


frontend = FrontEndApp()
frontend.run()

frontend.kv

<Scheduler>:
    schedule_text: schedule_text
    BoxLayout:
        orientation:'vertical'

        Label:
            text: "Schedule"
            font_size: 64
            color: 0.92, 0.45, 0
        Label:
            id: schedule_text
            text: "No"
            font_size: 21
        Button:
            text: "Update schedule"
            font_size: 32
            size: 100, 50
            #on_press: root.show_schedule()  # without `widget`
            on_press: root.show_schedule(self)  # with access to clicked button

PEP 8 -- Style Guide for Python Code