除了直接排序，还可以利用heaq模块的nlargest()和nsmallest()方法，例如：

>>> nums = [3, 5, 2, 4, 1]
>>> smallest = heapq.nsmallest(3, nums)
>>> print(smallest)
[1, 2, 3]
>>> largest = heapq.nlargest(3, nums)
>>> print(largest)
[5, 4, 3]

参考

Python Cookbook 1.4