input: Write a function to calculate the sum of the digits in a given number.
  def sum_digits(num):
      total = 0
      while num > 0:
          digit = num % 10
          total += digit
          num = num // 10
      return total
  
  assert sum_digits(12345)==15
  assert sum_digits(9876)==30
  assert sum_digits(101010)==3
  assert sum_digits(0)==0
  assert sum_digits(1)==1
output: def sum_digits(num):
      total = 0
      while num > 0:
          digit = num % 10
          total += digit
          num = num // 10
      return total