Pass variable from .py to .kv files

Question

I'm trying to develop an app using kivy and Python. I'm trying to pass a variable from a python function to kivy label. Evene if I look for a solution in the past answers, there wasn't the solution for my specific problem.

This is the Python code

from kivy.app import App
from kivy.uix.screenmanager import Screen, ScreenManager
from kivy.lang import Builder
from kivy.properties import ObjectProperty
from kivy.properties import StringProperty
import pandas as pd


class Home(Screen):
    pass

class Trends(Screen):
    provincia = ObjectProperty()

    def getdata(self):
        df = pd.read_csv("https://raw.githubusercontent.com/pcm-dpc/COVID-19/master/dati-province/dpc-covid19-ita-province.csv")
        prov = self.provincia.text
        r = df['denominazione_provincia']== prov
        nu = len(r)

        rows = []

        for check, row in zip(r, range(nu)):
            if check == True:
                rows.append(row)

        for n in rows:
            tot_casi = df.iloc[n]['totale_casi']
            date_casi = df.iloc[n]['data']

        casi = StringProperty(str(tot_casi))

        #variable i need to pass to label
        return print(casi)

    pass

class Autocertificate(Screen):
    pass

class News(Screen):
    pass

class Main(ScreenManager):
    pass

kv = Builder.load_file('my.kv')

class MyApp(App):
    def build(self):
        return kv

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

While this is my.kv:

Main:
    Home:
    Trends:
    News:
    Autocertificate

<Home>:
    name: 'Home'
    canvas.before:
        Rectangle:
            pos: 0, self.height/2
            size: self.width, self.height/2
            source: 'bg.png'

        Rectangle:
            pos: 0, 0
            size: self.width, self.height/2
            Color:
                rgba: (1, 1, 1, 1)

    GridLayout:
        rows: 8
        padding: [10, 10, 10, 10]


        Label:

        Label:
            text: 'Prevenire \nè meglio \nche curare.'
            font_size: 40
            color: 1, 1, 1, 1
            bold: True

        Label:
        Label:


        Button:
            on_release: app.root.current = "Autocertificate"
            color: 0.2, 0.6, 0.9, 1
            background_color: 1,1,1,0
            text: 'Autocertificazioni'
            font_size: 15

        Button:
            on_release: app.root.current = "Trends"
            color: 0.2, 0.6, 0.9, 1
            background_color: 1,1,1,0
            text: 'Contagi'
            font_size: 15


        Button:

            color: 0.2, 0.6, 0.9, 1
            background_color: 1,1,1,0
            text: 'Notizie'
            font_size: 15

        Button:

            color: 0.2, 0.6, 0.9, 1
            background_color: 1,1,1,0
            text: 'Chi Contattare'
            font_size: 15



<Trends>:
    name: 'Trends'
    provincia: prov
    canvas.before:
        Color:
            rgba: 1, 1, 1, 1
        Rectangle:
            pos: self.pos
            size: self.size
    GridLayout:
        padding: 10
        rows: 9
        GridLayout:
            cols:3
            Button:
                on_release: app.root.current = "Home"
                size: 60, 60
                size_hint: None, None
                Image:
                    source: 'back_white.png'
                    center_x: self.parent.center_x
                    center_y: self.parent.center_y
                    size_hint_y: None
                    height: dp(60)
            Label:
                text: 'Contagi'
            Label
            Label
        TextInput:
            id: prov
            hint_text: 'Inserisci la tua Provincia.'
            background_color: 1, 1, 1, 1
            size_hint: (.2, None)
            height: 30
            multiline: False
            background_color: 0,0,0,0.05
        GridLayout:
            cols:5
            Label:
            Label:
            Button:
                background_color: 0.1, 0.7, 0.9, 1
                text: 'Vedi Contagi'
                size_hint: None, None
                size: 100, 40
                pos: 200, 20
                on_press: root.getdata()
            #this below is the label i need to fill 
            Label:
            Label:
        Label:
        Label:
        Label:
        Label:
        Label:



<Autocertificate>:
    name: 'Autocertificate'
    canvas.before:
        Rectangle:
            pos: 0, self.height/2
            size: self.width, self.height/2
            source: 'bg.png'

        Rectangle:
            pos: 0, 0
            size: self.width, self.height/2
            Color:
                rgba: (1, 1, 1, 1)


<News>:
    name: 'News'
    canvas.before:
        Color:
            rgba: 0.2, 0.6, 0.9, 1
        Rectangle:
            pos: self.pos
            size: self.size
            size: self.size

what is the best practice to solve this?