input: from typing import List
  
  class SumOfDigits:
      
      def __init__(self, num: int):
          self.num = num
      
      def calculate_sum_of_digits(self) -> int:
          total = 0
          for ch in str(self.num):
              total += int(ch)
          return total
  
  """
  Example:
  for SumOfDigits(6342).calculate_sum_of_digits() == 15
  """
output:     
          def calculate_sum_of_digits(self) -> int:
              total = 0
              for ch in str(self.num):
                  total += int(ch)
              return total
  