array = [[4, 6,8],[7,[8, 7, 5],9]]
demo = []
def recursion(array):
	for i in array:
		if type(i) is list:
			demo.append(recursion(i))
		else:
			demo.append(i)

try:
	if list(array):
		recursion(array)

except err:
	print("not a valid array")

recursion(array)

result = []
for i in demo:
	if i is not None:
		result.append(i)

print(array, "-->", result)