v2ex blog answer

def grouper(group_membre_number, the_list, default=None):
    return map(default, *(iter(the_list), ) * group_membre_number)

def build_dict(group_list):
    result = {}

    for group in group_list:
        temp = iter(group[1:])
        result[group[0]] = dict(zip(temp, temp))

    return result

if __name__ == '__main__':
    l = range(1, 21)
    group_member_number = 5
    group_list = grouper(group_member_number, l)
    print group_list

    result = build_dict(group_list)
    print result

>>> python v2ex_group.py 
     [(1, 2, 3, 4, 5), (6, 7, 8, 9, 10), (11, 12, 13, 14, 15), (16, 17, 18, 19, 20)]
     {16: {17: 18, 19: 20}, 1: {2: 3, 4: 5}, 11: {12: 13, 14: 15}, 6: {9: 10, 7: 8}}