gistfile1.txt

#!/usr/bin/python3
import time
import random
from telethon import InteractiveTelegramClient
from telethon.tl.functions.photos import UploadProfilePhotoRequest
import os

client = InteractiveTelegramClient(
    'test1',
    '+400000000000',
    api_id=34057,
    api_hash='blabla'
)

photo_folder = 'blabla'

while True:
    photos = os.listdir(photo_folder)
    for photo in photos:
        input_file = client.upload_file(photo_folder + photo)
        result = client.invoke(UploadProfilePhotoRequest(input_file))
        print('Profile picture changed to {}.'.format(photo))
        time.sleep(45)

You have to call UpdateProfilePhotoRequest after you've uploaded the input file as a photo.