output_buf_size = 0
while True:
    output_buf = ctypes.create_unicode_buffer(output_buf_size)
needed = _GetShortPathNameW(long_name, output_buf, output_buf_size)
if output_buf_size >= needed:
    return output_buf.value
else:
    output_buf_size = needed
How to get Windows short file name in python?