negative = posneg_calcsums([item for item in items if item < 0])
for n in sorted(positive, reverse=True):
    if -n in negative:
        return positive[n] + negative[-n]
else:
    return None
print(posneg([-1, 1, -4, 5]))
print(posneg([6, 44, 1, -7, -6, 19]))
remove numbers from a list without changing total sum