Error: Destination path '/home/jupyter/.fastai/data/mnist_sample/train/3/50560.png' already exists

I am trying to move some files from source path to destination path. The program works, the files are able to be moved. But when i run it again to use the "if" statement to check if the files exist - it gets skipped over and goes straight to shutil.move(s, destination) again.

Kindly seeking any advice

source = '/home/jupyter/.fastai/data/mnist_sample/valid/3/'
destination = '/home/jupyter/.fastai/data/mnist_sample/train/3/'

files_to_move = ['50560.png',  '57306.png',  '983.png']

for file in files_to_move:
    s = source + file
    d = destination + file
    print(d)

if s in source:
    print("exist")
    
else:
    print("File is moving")
    shutil.move(s, destination)
    print('Moved:', file)


> Ideal output after moving the files and running it again
exist
exist
exist

> Output I get as an error
File is moving
Error: Destination path '/home/jupyter/.fastai/data/mnist_sample/train/3/50560.png' already exists