input: Write a python function to calculate the sum of a given list of odd numbers.
  assert sum_odd_numbers([1, 3, 5, 7, 9]) == 25
  assert sum_odd_numbers([11, 13, 15, 17]) == 56
  assert sum_odd_numbers([2, 4, 6]) == 0
output: def sum_odd_numbers(numbers):
      return sum(num for num in numbers if num % 2 != 0)