input: Write a function to calculate the sum of the digits in a given number. If the given number is negative, ignore the negative sign and return the sum of the digits. If the given number is zero, return zero.
  assert sum_digits(123)==6
  assert sum_digits(456)==15
  assert sum_digits(-789)==24
  assert sum_digits(0)==0
  assert sum_digits(1001)==2
output: def sum_digits(n):
      n = abs(n)
      return sum(int(digit) for digit in str(n))