将变量从.py传递到.kv文件

Question

我正在尝试使用kivy和Python开发应用程序。我正在尝试将变量从python函数传递给kivy标签。即使我在过去的答案中寻找解决方案，也没有针对我特定问题的解决方案。

这是Python代码

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()

这是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

解决此问题的最佳做法是什么？