import itertools
A = [[1, 2], [2, 3], [1, 2, 3], [3, 4, 5], [2, 2, 1]]
tuples = itertools.zip_longest(*A)
for t in tuples:
    s = [x for x in t if x is not None]
print(sum(s) / len(s))
Среднее значение списка неравных списков