不能用for while循环，求做法

函数接收字符串s，要求模拟s.low()功能并返回处理后的新字符串

def lowercase(word):
    if word == '':  
        return ''
    else:
        letter = ord(word[0])      
        if letter in range(65, 91):      
            return chr(letter + 32) + lowercase(word[1:])     
        elif letter in range(97, 123):
            return chr(letter) + lowercase(word[1:])

WORD = str(input("Enter a word: "))
print(lowercase(WORD))

s.low()函数吗，应该是s.lower()函数吧