如何在不同位数的列表中生成4位的python组合？

def generate_combinations(nums, current_combination, result):
    if len(current_combination) == 4:
        result.append(current_combination)
        return
    
    for num in nums:
        new_combination = current_combination + [num]
        generate_combinations(nums, new_combination, result)

def generate_4_digit_combinations(nums):
    result = []
    generate_combinations(nums, [], result)
    return result

# 示例用法
nums = [1, 2, 3, 4, 5, 6, 7, 8, 9]
combinations = generate_4_digit_combinations(nums)
print(combinations)