def sum_of_digits(s):
  letters = []
  numbers = []

  for i in s:
    if i.isalpha():
     letters.append(i)
    elif i.isdigit():
      numbers.append(i)
  print("The extracted non-digits are: {} ". format(letters), end="\n")
  print("The sum of digits operation performs ", "".join(numbers))

sum_of_digits("1aw4")