案例：手动输入一个字符串，所有字符反转，大小写相互转

string = input('请输入一个字符串：')
lists = list(string)
print('输入的字符串：', lists)
lists.reverse()
print('反转后的字符串：', lists)
i = 0
while i < len(lists):
    if 'a' <= lists[i] <= 'z':
        lists[i] = lists[i].upper()
    elif 'A' <= lists[i] <= 'Z':
        lists[i] = lists[i].lower()
    i += 1
print('大小写改变的字符串：', lists)