How to call a variable from another class from one class?

Question

Python

Hi I have code:

import pyowm
from pyowm.owm import OWM
from pyowm.utils.config import get_config_from

from kivy.lang import Builder
from kivy.uix.floatlayout import FloatLayout

from kivymd.uix.button import MDIconButton
from kivymd.app import MDApp
from kivymd.uix.tab import MDTabsBase


config_dict = get_config_from('config.json')
owm = pyowm.OWM('ed3d1e950f0d1e73b26cfd7f55fbb4f9', config_dict)

mgr = owm.weather_manager()

kv = '''
BoxLayout:
    orientation: "vertical"

    MDToolbar:
        title: "View Allthings"
        MDIconButton:
      	icon: "youtube"
   		 theme_text_color: "Custom" 
    		md_text_color: 2, 9, 6, 1
    		icon_size: 1.2, 1.9
    		on_press: app.on_start()
      
    MDTabs:
        id: tab
    

<w>:
  FloatLayout:
      id: fl	
      MDTextField:
      	hint_text: "Название города"
      	text: ""
      	mode: "rectangle"
      	id: ccity
      	pos_hint: {'y': .90, 'x': .3}
      	size_hint: .4, .067
    MDIconButton:
      	icon: "check-bold"
      	pos_hint: {'y': .89, 'x': .75}
      	on_press: root.update()
      	
      	
      	
      	
  MDGridLayout:
    rows: 4
    size_hint_y: .8
    spacing: 200
    padding: 30
    pos_hint: {'y': .03, 'x': .05}
    MDIcon:
      icon: "thermometer-low"
    MDIcon:
      icon: "check-bold"
    MDIcon:
      icon: "twitter"
         MDIcon:
      icon: "discord"
  
  MDGridLayout:
    cols: 2
      rows: 4
    spacing: 100
    size_hint: .9, .8
    md_bg_color: 0, 0, 0, .2
    pos_hint: {'y': .03, 'x': .05}
      MDLabel:
      	id: label
          text: "         Температура сейчас"
          halign: "center"
      MDLabel:
      	id: res
      	text: "None"
          halign: "center"
      MDLabel:
          id: label2
          text: "Min/max "
          halign: "center"
      MDLabel:
          id: res4
          text: "None"
          halign: "center"
      MDLabel:
          id: label4
          text: "Tab"
          halign: "center"
      MDLabel:
          id: res1
          text: "None"
          halign: "center"
      MDLabel:
          id: label6
          text: "Tab"
          halign: "center"
      MDLabel:
          id: res2
          halign: "center"
'''
    
class w(FloatLayout, MDTabsBase):
  def update(self):
      if (self.ids.ccity.text == ""):
      	city = "Ню Йорк"
      else:
        city = str(self.ids.ccity.text)
      observation = mgr.weather_at_place(city)
      w = observation.weather
      l = w.temperature('celsius')['temp']
      temp = str(l) + " °C"
      self.ids.res.text = str(temp)

class k(FloatLayout, MDTabsBase):
  pass

ws = w()

class Main(MDApp):
    n = 3
    def build(self):
        return Builder.load_string(kv)
    
    def on_start(self):
    	file = open('city.txt', 'r', encoding='utf-8')
    	nms = ["Курс биткоина", "Курс доллара и эвро", "Коронавирус", "Погода"]
    	w1 = self.root.ids.tab.add_widget(w(text=nms[self.n]))
    	self.n -= 1
    	w2 = self.root.ids.tab.add_widget(k(text=nms[self.n]))
    	txtc = str(file.read())
    	pass
    	

if __name__ == '__main__':
  Main().run()

I need a variable from the Main(txtc) class to be set in the TextField (it's in the "w" class) at startup.
Do not pay attention to file.load

Answer 1

main(txtc). Not in this code. The txtc variable does not belong to the Main class either. You need to either store the variable in the global scope. Or make txtc a variable of the Main class and call it through the Main object.