py3: use list of bytes rather than bytestring while extending bytes into lists Python 2: >>> ls = [] >>> ls.extend(b'abc') >>> ls ['a', 'b', 'c'] Python 3: >>> ls = [] >>> ls.extend(b'abc') >>> ls [97, 98, 99] So to make sure things work fine in Py3, this patch does: >>> ls = [] >>> ls.extend([b'a', b'b', b'c']) >>> ls [b'a', b'b', b'c'] After this `hg log -G` works!