Want To Display Random File From Folder With Kivy (Python)

I have this folder full of images and I need to be able to display a random file from the folder each time I run the app, currently I have the file saved under the variable flagfile and don't seem to be getting an error when I run this code. For some reason the image doesn't end up displaying on the actual app though I'm new to kivy and was hoping for help.

My Code so far:
Python

import kivy
from kivy.app import App
from kivy.uix.widget import Widget
from kivy.properties import ObjectProperty
from kivy.lang import Builder 
from kivy.uix.image import Image
import random
import os
from kivy.core.window import Window
import numpy as np
from kivy.properties import StringProperty
from kivy.uix.floatlayout import FloatLayout


class MyLayout(Widget):
    pass 


   

class colorApp(App):

    flagfile = StringProperty()
    def source_getter(self):
        path = "/Users/samarth/Downloads/App/w320"
        files = os.listdir(path)
        self.flagfile= random.choice(files)
        
    def build(self):
        Window.clearcolor = (1,1,1,1)
        return MyLayout()


    
if __name__ == "__main__":
    colorApp().run()
   `

Kivy

<MyLayout>    
    BoxLayout:
        orientation: "vertical"
        size: root.width, root.height

        padding: 50
        spacing: 20
        Image:
            id: cardimage
            source: app.flagfile
                
            on_source: print(self.source)
        Button:
            text: "Hello World"`
    

You didn't write the correct path. You just typed the filename. Change this line:

self.flagfile = random.choice(files)

to

self.flagfile = path + "\\" + random.choice(files)

and you don't need do that but it's more efficient: You can change your path like this: path = os.path.join(os.path.expanduser('~'), 'Downloads', 'App', 'w320')

you need only to concatenate the file path, os.listdir return a list of file names (without the complete path).

def source_getter(self):
        path = "/Users/samarth/Downloads/App/w320"
        files = os.listdir(path)
        self.flagfile= path + '/' + random.choice(files)

I hope this helps.