写一个Python函数，给定一个整数列表，计算列表中的奇数之和。


[1, 2, 3, 4, 5, 6, 7, 8, 9]
```python
def sum_odd_numbers(numbers):
    return sum(num for num in numbers if num % 2 != 0)

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9]
odd_sum = sum_odd_numbers(numbers)
print(odd_sum)
```
输出结果为：25