def recursive_list_sum(data_list):
	total = 0
	for element in data_list:
		if type(element) == list:
			total = total + recursive_list_sum(element)
		else:
			total = total + element

	return total

import itertools

list2d = [[1, 2, 3], [4, 5, 6], [7], [8, 9]]
# a = list(itertools.chain.from_iterable(list2d))  # call staticmethod from_iterable
a = list(itertools.chain(*list2d))   # init an object
b = sum(list2d, [])
print(a, b)