如何创建3个简单的函数来返回隔离字符，返回重复字符，以及返回删除了#comment的字符串？

def isolate_characters(string):
    isolated_chars = ''
    for char in string:
        if char.isalpha():
            isolated_chars += char + ' '
    return isolated_chars.strip()

def find_duplicate_characters(string):
    duplicate_chars = ''
    for char in string:
        if string.count(char) > 1 and char not in duplicate_chars:
            duplicate_chars += char + ' '
    return duplicate_chars.strip()

def remove_comment(string):
    return string.replace('#comment', '')