If-Else functions practice - Python

追加: 2026-05-12

[00:00:01][sighs] >> Hi guys. Today we'll be working on if else statements. So the task for today is to create a function get letter grade that asks a user for a score from between 0 and 100 and converts it into a letter grade where A is 90 and above, B is 80 to 89 and so on and so forth where all the inputs are floats.

[00:00:23]So, the first thing to do of course is to define a function called get letter grade.

[00:00:31]letter grade, which takes in a score. Which we can just call score.

[00:00:39]So, a lot of beginners start by doing this where they ask if score is greater than or equal to 60. And if it is, they will return D.

[00:00:52]But watch what happens. If I pass an 85 here for example, and I put 85 as the score, it'll check that 85 is indeed greater or equal to 60. So, it will immediately return D. But that's completely wrong since 85 should be a B.

[00:01:10]And here's the key idea. Python actually reads code from top to bottom. The moment it finds a condition that's true, it runs it and it stops checking everything else. So, if you start from the bottom, higher grades will never get a chance to be checked. So, instead, we actually need to flip the order. And let's say put this as 90.

[00:01:29]And let's put this as return A.

[00:01:33]So, we start from the highest grade first.

[00:01:36]Uh next thing we can do is uh check the next highest grade using elif. So, let's say if it's not 90, it'll check if it's greater or equal to 80, it will return B.

[00:01:55]And we could check this actually for the remaining conditions from um C to D actually. However, for F we will have to type um an else statement cuz that is actually the last grade that can be achieved.

[00:02:12]So, if score greater or equal to 60 return D.

[00:02:20]Oops.

[00:02:22]So, for F uh since it'll check if none of these conditions are true, what's the last thing it can be? So, let's say it's like a score of 59. It'll check if it's greater or equal to 90 and it's not and it's not greater or equal to 80, not greater or equal to 70, not greater or equal to 60. So, that's why we just have an else statement here and it will be returning F.

[00:02:47]So, this is actually the final code and uh let's actually just uh walk through it with a B5. So, um let's first just create an input. So, let's say score is an input where we can enter a score.

[00:03:13]Um and the grade is equal to um whatever the score inputted into the function is and we can just pro- go ahead and actually print that.

[00:03:29]Okay, so it's going to ask us to enter a score.

[00:03:33]Let's just check with 85.

[00:03:35]And as it turns out, it ends up being B, which is indeed in between 80 and 89.