What does Quick Sort look like in Python?

　　Let's talk about something funny at first.

　　Have you ever implemented the Quick Sort algorithm all by yourself before?If your answer is NO,

please do it first before you continue reading the following lines. I have learned and implemented

the Quick Sort algorithm many times in a lot of courses like Data Structure, Algorithm and some other

courses online. But unfortunately, I always forgot how to implement it after a really short time.

　　... ...

　　The good news is that I'll not forget it again.(I hope so.) The reasons are as follows:

def qs(arr):
    if not arr:
        return []
    return qs([x for x in arr[1:] if x <= arr[0]]) + arr[:1] + qs([x for x in arr[1:] if x > arr[0]])

　　WOW, what happened? It's so amazing that the most important part of the algorithm is

implemented IN ONLY ONE SINGLE LINE. Do you believe that and can you remember it?

References:

1. 我为什么要学习Python？ http://www.kaifazhe.com/python/874.html