仅使用递归在python中返回包含数字组合的列表

def get_combinations(digits):
    # 定义递归的终止条件
    if len(digits) == 0:
        return []

    # 获取当前数字对应的字母集合
    digit_map = {
        '2': ['a', 'b', 'c'],
        '3': ['d', 'e', 'f'],
        '4': ['g', 'h', 'i'],
        '5': ['j', 'k', 'l'],
        '6': ['m', 'n', 'o'],
        '7': ['p', 'q', 'r', 's'],
        '8': ['t', 'u', 'v'],
        '9': ['w', 'x', 'y', 'z']
    }
    current_digit = digits[0]
    letters = digit_map[current_digit]

    # 递归调用，获取剩余数字的组合列表
    remaining_combinations = get_combinations(digits[1:])

    # 组合当前数字的字母与剩余数字的组合列表
    combinations = []
    if len(remaining_combinations) == 0:
        combinations = letters
    else:
        for letter in letters:
            for combination in remaining_combinations:
                combinations.append(letter + combination)

    return combinations

# 测试示例
digits = '23'
result = get_combinations(digits)
print(result)