input: Write a class to calculate the sum of the digits of a given number.
  
  class SumOfDigits:
      
      def __init__(self, num):
          self.num = num
      
      def calculate_sum_of_digits(self):
          total = 0
          for ch in str(self.num):
              total += int(ch)
          return total
  
  assert SumOfDigits(6342).calculate_sum_of_digits() == 15
  assert SumOfDigits(12345).calculate_sum_of_digits() == 15
  assert SumOfDigits(987).calculate_sum_of_digits() == 24
  assert SumOfDigits(54321).calculate_sum_of_digits() == 15
  assert SumOfDigits(0).calculate_sum_of_digits() == 0
output: def calculate_sum_of_digits(self):
      total = 0
      for ch in str(self.num):
          total += int(ch)
      return total