题解 | #字符个数统计#

list = []
for i in range(len(n)):
    if i in list:continue
    else:
        if ord(n[i])>=0 and ord(n[i])<=127: #查看ASCII码，筛选满足范围的字符
            if n[i] in list: #去重
                continue
            else:
                list.append(n[i])
        else:break
print(len(list))