如何编写一个包含字母和数字的转换(小写->大写，一位数->两位数，两位数->数位之和)程序？

def lowercase_to_uppercase(char):
    return char.upper()

def one_digit_to_two_digits(num):
    if num < 10:
        return '0' + str(num)
    else:
        return str(num)

def sum_of_digits(num):
    tens_digit = num // 10
    units_digit = num % 10
    return tens_digit + units_digit

def convert_string(input_string):
    converted_string = ''
    for char in input_string:
        if char.islower():
            converted_string += lowercase_to_uppercase(char)
        elif char.isdigit():
            num = int(char)
            if num < 10:
                converted_string += one_digit_to_two_digits(num)
            else:
                converted_string += str(sum_of_digits(num))
        else:
            converted_string += char
    return converted_string

input_string = input("请输入字符串：")
output_string = convert_string(input_string)
print("转换后的字符串为：", output_string)