Assignment Two and Test Two Results

In a previous blog post, I was discussing a test case error I had in my second assignment. Someone was kind enough to post some test cases for me to try out with the star node. I tried them out and passed all of them. When the results arrived on MarkUs, I was finally able to see the test suite and find exactly where I went wrong. Here was my code for the star node:

if r.symbol == '*':
     return s == '' or any(root_match(r.children[0], s[:i]) and
                                     root_match(r, s[i:]) for i in range(len(s) + 1))

The code failed on regex_match(RegexTree('e*'), '0'), it produces an infinite loop in this case. The key here is the splicing index. My method calls itself with the same string and same regextree, which indeed produces a stack overflow of recursive calls. After investigating, I found the correct code to be:

if r.symbol == '*':
     return s == '' or any(root_match(r.children[0], s[:i]) and
                                     root_match(r, s[i:]) for i in range(1, len(s) + 1))

That's right. The code is nearly identical except the index starts at one instead of zero. Ouch. Since my code worked on more complex test cases I naturally assumed that it would work on simpler cases. This goes to show that you should always check simpler cases in your own code and make sure they work perfectly.

On the bright side, I managed to ace the last test for my first 100% on a midterm at U of T. Hopefully there will be many more to come. I hope everyone is enjoying the course and I wish everyone the best of luck in their course work. Cheers!