编写一个Python函数，该函数接受一个列表作为输入，并返回列表中第二个最小的数字。
   
[4, 8, 1, 9, 5, 3]
以下是一个实现该功能的Python函数：

```python
def second_smallest(numbers):
    smallest = float('inf')
    second_smallest = float('inf')
    for number in numbers:
        if number < smallest:
            second_smallest = smallest
            smallest = number
        elif number < second_smallest:
            second_smallest = number
    return second_smallest
```
使用它，您可以得到：

```python
numbers = [4, 8, 1, 9, 5, 3]
second_smallest_number = second_smallest(numbers)
print(second_smallest_number)
# 输出：3
```