input: Write a function to create a class that takes a given number and calculates the sum of its digits. The class should have a method to perform this calculation and return the sum.
  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
  
  digit_sum = SumOfDigits(6342)
  result = digit_sum.calculate_sum_of_digits()
  assert result == 15
  
  digit_sum = SumOfDigits(12345)
  result = digit_sum.calculate_sum_of_digits()
  assert result == 15
  
  digit_sum = SumOfDigits(98765)
  result = digit_sum.calculate_sum_of_digits()
  assert result == 35
  
  digit_sum = SumOfDigits(101)
  result = digit_sum.calculate_sum_of_digits()
  assert result == 2
  
  digit_sum = SumOfDigits(0)
  result = digit_sum.calculate_sum_of_digits()
  assert result == 0
output: 
  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
  