Yeah, this behavior might be because Python doesn't store unicode string as it is. AFAIK Python always store string as an array of fixed-sized bytes for random access. In other words, the size of an element of the array is the same as the maximum size of characters in the string, meaning that even a character of 1 byte ASCII can be stored as 4 bytes.

So when one side is bytes (filetype in this case) and the other side is a string, the underlying byte representation can be different even if they represent as the same string in higher level.