对于嵌套的for循环，有没有更好的替代方案？

# 原始嵌套for循环
result = []
for i in range(3):
    for j in range(3):
        result.append((i, j))

# 使用列表推导式
result = [(i, j) for i in range(3) for j in range(3)]

# 使用生成器表达式
result = ((i, j) for i in range(3) for j in range(3))

import itertools

# 使用itertools.product
result = list(itertools.product(range(3), range(3)))

def nested_loops(levels, current=[]):
    if levels == 0:
        print(current)
    else:
        for i in range(3):
            nested_loops(levels - 1, current + [i])

nested_loops(2)

import numpy as np

arr = np.arange(9).reshape(3, 3)
result = [(i, j) for i in arr for j in i]