统计字母数字和特殊字符的个数

源程序：

print("请输入一串字符(包含大小写字母、数字和其他字符)：")
str1 = input()

upp_num = 0
low_num = 0
digit = 0
other = 0

for i in str1:
    if "a" <= i <= "z":
        low_num += 1
    elif "A" <= i <= "Z":
        upp_num += 1
    elif "0" <= i <= "9":
        digit += 1
    else:
        other += 1
print("小写字母 ：", low_num, " 个。", "\n大写字母：", upp_num, " 个。")
print("\n数字 ：", digit, " 个。", "\n其他字符：", other, " 个。")