input: Write a function to calculate the sum of the digits in a given number. The function should return the sum of all the digits in the number. If the number is negative, still calculate the sum of the digits.
  
  assert sum_digits(123) == 6
  assert sum_digits(100) == 1
  assert sum_digits(9999) == 36
  assert sum_digits(-1234) == 10
  assert sum_digits(0) == 0
output: def sum_digits(n):
      return sum(int(digit) for digit in str(abs(n)))