生成一个文件，其中包含所有可能的组合字符串，字符串长度为0,1，且不带itertools

def generate_combinations(current_string, length, charset):
    # 递归终止条件：当当前字符串的长度等于目标长度时，将当前字符串写入文件
    if len(current_string) == length:
        with open('combinations.txt', 'a') as file:
            file.write(current_string + '\n')
        return

    # 递归生成所有可能的组合字符串
    for char in charset:
        generate_combinations(current_string + char, length, charset)
        generate_combinations(current_string, length, charset)

charset = 'abcdefghijklmnopqrstuvwxyz'
length = 1  # 字符串长度为1

generate_combinations('', length, charset)