input: 
  class SumOfDigits:
      
      def __init__(self, num):
          self.num = num
      
      def calculate_sum_of_digits(self):
          """
          Calculate and return the sum of the digits of the given number.
          >>> SumOfDigits(6342).calculate_sum_of_digits()
          15
          """
          total = 0
          for ch in str(self.num):
              total += int(ch)
          return total
  
output:     
          total = 0
          for ch in str(self.num):
              total += int(ch)
          return total
  