gistfile1.py

import Queue

a = [1, [2], [3], [4,5]]

q = Queue.Queue()

res = []

def copy_arr_to_q(arr, q):
    for item in arr:
        q.put(item)

copy_arr_to_q(a, q)

while not q.empty():
    element = q.get()
    if type(element) is list:
        copy_arr_to_q(element, q)
    else:
        res.append(element)

print(res)