Gеtting an error while choosing random file from directory

I am trying to choose a random .PNG file from directory - there are 5 PNG files (1,2,3,4,5/png)

Python version is 3.8.2

Here is my code:

import os
import random

file_path = random.choice(os.listdir(r"C:/Users/katherine/Desktop/testphotos"))
client.users_setPhoto(image=file_path)

But I get an error something about "there is no such file"

Traceback (most recent call last):     
File "C:/Users/katherine/Desktop/testcode/main.py", line 14, in <module>
        client.users_setPhoto(image=file_path)     
File "C:\Users\katherine\AppData\Local\Programs\Python\Python38-32\lib\site-packages\slack\web\client.py", line 1638, in users_setPhoto
        return self.api_call("users.setPhoto", files={"image": image}, data=kwargs)     
File "C:\Users\katherine\AppData\Local\Programs\Python\Python38-32\lib\site-packages\slack\web\base_client.py", line 171, in api_call
        return self._event_loop.run_until_complete(future)     
File "C:\Users\katherine\AppData\Local\Programs\Python\Python38-32\lib\asyncio\base_events.py", line 616, in run_until_complete
        return future.result()     
File "C:\Users\katherine\AppData\Local\Programs\Python\Python38-32\lib\site-packages\slack\web\base_client.py", line 207, in _send

f = open(v.encode("ascii", "ignore"), "rb")  

FileNotFoundError: [Errno 2] No such file or directory: b'3.png'

Process finished with exit code 1