codecs.StreamRecoder.writelines is implemented as:

    def writelines(self, list):

        data = ''.join(list)
        data, bytesdecoded = self.decode(data, self.errors)
        return self.writer.write(data)

It can't take a list of bytes because then the ''.join throws an error, and it can't take a list of str because self.decode takes bytes.

It looks like bytes are intended (self.write takes bytes), so I'll submit a simple PR to fix this.