Originally Posted by kovidgoyal
It's just huffman coding, a public domain algorithm, with a few implementation winkles. Frankly, I don't see any difference between "a mathematical description" and a "source code description" since both use a language to describe an algorithm.
The python code is based on copyrighted code that has probably been accessed in a way that somebody can have legal opinions about. If I just copy the Python code it I am not sure it can be GPL:ed. And I am very unsure if the GPL notice in the Python code is correct.
A mathematical description from which I do an implementation were I do not look at existsing copyrighted code is definitely unproblematic.