test.py

from kivy.lang import Builder

from kivymd.app import MDApp

KV = '''
Screen:
    BoxLayout:
        orientation: 'vertical'
        size_hint_y: None
        canvas.before:
            Color:
                rgba: (1, 0, 0, 0.5)
            Rectangle:
                size: self.size
                pos: self.pos
        MDSlider:
            min: 0
            max: 100
            value: 40
            on_touch_up: app.print_test()
'''


class Test(MDApp):
    def build(self):
        return Builder.load_string(KV)

    def print_test(self, *args):
        print("TOUCH UP")


Test().run()