flatten_nested_list.py

# sum_n if number from list is even number
sum_n = 0

# glued list from nested lists
glued = []

# nested list of integers
nums = [[2,4,[333, [-22, [90, 91], -44],666],6], 10, 3, [17,19,20], [63,42,32,30]]

def gluelist(nms, lst):
    global sum_n
    for n in nms:
        if not isinstance(n, list):
            lst.append(n)
            if n % 2 == 0:
                sum_n += n
                # print(n, end="+")
        else:
            gluelist(n, lst)

gluelist(nums, glued)
print()
print(glued)
print(sum_n)