File isn't deleted after move

I want to change directory for just created file and delete it from old directory. File is moved, but in old directory file isn't deleted as I expect, why? I tryed to change my code, so when file is created in advace it's deleted with no problem.

import shutil
src = 'D:\w\Pack.txt'
dst = 'D:\w\StrangeFolder\Pack.txt'
filename = "Pack.txt"

with open(filename, 'w') as f:
    shutil.move(src, dst)
    shutil.rmtree(filename)