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Python Python Basics (Retired) Things That Count Exceptions

Posted by Oleksii Kukharyshyn
Oleksii Kukharyshyn
470 Points

Does the program understand everything under 1 as percentage of the word, but everything over 1 as a number of letter?

Case: I've wrote the same code as in video, checked it a few times and tested for different numbers. Problem: some of the float numbers under 1 and every float over 1 return an error. Checked words: "Magic" and "Alex" (short for my name). Problem numbers: 0.9 for "Alex", all float numbers from 1.1 to 2.9 for "Alex", to 3.9 for "Magic". It looks like the round() doesn't work properly, but I'm sure I wrote it just like in the video. Code:

user_string = input("What's your word? ")
user_num = input("What's your number? ")

try:
  our_num = int(user_num)
except:
  our_num = float(user_num)

if not "." in user_num:
  print(user_string[our_num])
else:
  ratio = round(len(user_string)*our_num)
  print(user_string[ratio])

What exactly did I miss?

3 Answers

Stephen Link
Stephen Link
3,685 Points
Stephen Link
Stephen Link
3,685 Points

You aren't getting errors because round() isn't working but rather because of how it is being used. In this program the idea is that you enter some float less than 1 to get a percentage of the word's length. If you enter a number greater than 1, and then multiply this by the length of the string, you will most likely wind up with a number which is larger than the length of the string. If a string only has 5 characters you can't access a character at any position higher than 4 [strings start addressing at 0] because the character just doesn't exist.

0.9 is giving you problems on "Alex" because the length of Alex is 4, and 4 * 0.9 = 3.6, and this is rounded up to 4. Since we start at index 0 there is no location 4 in "Alex" and therefore you get an error when you ask for the letter in that location.

Kenneth Love
STAFF
Kenneth Love
Treehouse Guest Teacher
Kenneth Love
Kenneth Love
Treehouse Guest Teacher

Yeah, it's not a perfect program :) It's more for illustrating how to work with numbers and strings at the same time than it is how to build an amazing piece of software. Ideally, you'd make sure that no number greater than 1 came in for a float (or that you looped around the word however many times needed) and that any integer you ended up with would be lower than the len() of the word.

All of that, though, is way too much to go over or expect students to do in such a basic course.

Oleksii Kukharyshyn
Oleksii Kukharyshyn
470 Points
Oleksii Kukharyshyn
Oleksii Kukharyshyn
470 Points

Thanks a lot! It is still a bit confusing for me, but I now understand it, more or less. I thought of limiting the possible answers to second question, but doing this from a technical side (not just by asking user to write a number from 0 to (len(user_string)-1)), but I guess, it would really be an overcomplication at this point.