DoubleYouEl

def decode(msg):
    text = ""
    for i in range(0, len(msg), 2):
        text += unrot(msg[i: i + 2], i // 2)                    # add position as extra parameter
    return text


def unrot(pair, pos, key=ord('x')):
    if pos % 2 == 0:                                            # "even" position => 2nd char is offset
        pair = pair[1] + pair[0]                                # swap letters in pair