arr = []  # contains input data

while True:

   try:  # checking for the correct input data

       n = int(input('number: '))

   except:

       print('An integer must be entered!')

       continue

   if n == 0:  # stopping data entry

       break

   else:

       arr.append(n)

print(arr)

neg_sum, pos_sum = 0, 0

for number in arr:  # iterating through all the list elements

   if number < 0:

       neg_sum += number

   else:

       pos_sum += number

print('Sum of negative numbers:', neg_sum)

print('Sum of positive numbers:', pos_sum)

Более упрощенный вариант:

arr = []  # contains input data

while True:

   n = int(input('number: '))

   if n == 0:  

       break

   else:

       arr.append(n)

neg_sum = 0

pos_sum = 0

for number in arr:  # iterating through all the list elements

   if number < 0:

       neg_sum += number

   else:

       pos_sum += number

print('Sum of negative numbers:', neg_sum)

print('Sum of positive numbers:', pos_sum)