如何将集合的元素组合成N个部分的所有组合？

def combine(nums, N):
    if N == 1:
        return [nums]
    elif N > len(nums):
        return []
    elif N == len(nums):
        return [[num] for num in nums]
    else:
        result = []
        for i in range(len(nums)):
            num = nums[i]
            rest = nums[i+1:]
            res = combine(rest, N-1)
            for r in res:
                result.append([num] + r)
        return result

# 示例用法
nums = [1, 2, 3, 4]
N = 2
result = combine(nums, N)
print(result)