Jump to second part, the first part illustrate how did I found the problem, which is not interesting at all.
How did I find this problem
Recently, my roommate is practicing for interview with Leetcode, he keeps coming to ask for my help with some problems. The problems in Leetcode are really easy (especially when compared with problems in OJs oriented for ACM), but if you keep sensitive, it could still help you find some corner in the language that you would never notice otherwise.
Here is my log about investigating difference of
range() between python2 and python3 - and their different against