test.py

from kivy.app import App
from kivy.lang import Builder
from kivy.properties import ObjectProperty
from kivy.uix.dropdown import DropDown
from kivy.uix.screenmanager import ScreenManager, Screen


class WeatherDropDown(DropDown):
    locw = ObjectProperty()

    def on_select(self, x):
        self.locw.dropbutton.text = x


class LocationAndWeatherScreen(Screen):
    dropbutton = ObjectProperty()

    def on_dropbutton(self, *args):
        self.dropdown = WeatherDropDown(locw=self)
        self.dropbutton.bind(on_release=self.dropdown.open)


class DropDownExampleApp(App):
    def build(self):
        self.manager = ScreenManager()
        self.manager.add_widget(LocationAndWeatherScreen())
        return self.manager


Builder.load_string("""
<WeatherDropDown>:
    Button:
        text: 'cold'
        on_press: root.select('cold')
    Button:
        text: 'hot'
        on_press: root.select('hot')

<LocationAndWeatherScreen>:
    dropbutton: dropbutton
    BoxLayout:
        orientation: 'vertical'
        Button:
            id: dropbutton
            text: 'Weather'
            size_hint_y: 0.2
        Widget:
            id: filler
""")


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