Creating a sequentially joined list using a for loop in Python

I need help creating a new list z, where I will have list values as y0, x0, y1, x1, y2, x2, y3 in vertical order as an array.

output: z = [1, 1, 1, 0, 0, 2, 2, 2, 2, 4, 4, 3, 3, 3, 8, 8, 4, 4, 4]

I tried this for loop iteration, but instead of the desired list z, I get only list values as y2, x2.

I really appreciate any help you can provide.

x = [[0, 0], [4, 4], [8, 8]]
y = [[1, 1, 1], [2, 2, 2], [3, 3, 3 ], [4, 4, 4]

for i in range (0, 3):
    z = [*y[i], *x[i]]

Answer

I found the solution as:

from heapq import merge
from itertools import count

x = [[1, 1, 1], [2, 2, 2], [3, 3, 3 ], [4, 4, 4]]
y = [[0, 0], [4, 4], [8, 8]]
counter = count()
z = np.hstack(list(merge(x, y, key=lambda x: next(counter))))