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Instructor: Welcome back.

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Let's do an exercise where we check

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for duplicates in a list.

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So I have some_list here,

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and I want you to be able to check this list

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and print whatever the duplicate values are.

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In this case, we see that 'n' has duplicates

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and also 'b' has duplicates.

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So I want you to print 'b' and 'd' as a list in here.

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How would you go about doing that?

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Pause the video, give it a go,

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otherwise, I'm gonna keep going with the answer.

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And by the way, you're not allowed to use sets for this.

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So for this exercise, you can't use the data structure sets.

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Instead, you have to just use conditionals and loops

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that we've learned in the past couple of videos.

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So give it a try, pause the video, and when you're ready,

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I'm gonna go ahead with the answer.

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First, I'm going to create a variable called duplicates,

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and this is going to be an empty list

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that we're gonna populate with any duplicate values.

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Next, I'm going to loop over this list,

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so I'm going to say for value in some_list.

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And in here, well, what can we do?

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This is a tough one, but what I'm going to do

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is say if some_list.count.

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Remember, count allows us to count

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how many times an item in a list exists.

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And I'm going to say value so that some_list.count,

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and I give it 'a', it's going to count for me

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how many times 'a' happens in the list.

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Very, very useful.

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Again, if you didn't come up with that,

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there's many solutions to this problem.

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So there's no one right answer.

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I'm just showing you how I would've done it.

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Now here, I'm going to say if that's greater than 1.

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In that case, that means there's a duplicate.

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So I'm going to add it inside of the duplicates.

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So let's just go ahead and say .append

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because I wanna append, and in here say value.

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And at the end of all this, let's just print duplicates.

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Now, let's see if this works.

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I'm going to click run, and, all right,

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I get both 'b' and 'n', but I don't need this duplicates.

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I just need to know what are the duplicates.

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I just need one instance of 'b' and one instance of 'n'.

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So what we can do here is do another if statement

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and say if value is not in duplicates.

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And, yes, this is a bit of a trick.

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You may remember that not is the opposite, right.

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So we're checking, "Hey, is value in duplicates?"

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And not essentially says, "Hey, if value

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is not in duplicates it reads like English."

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And this is going to evaluate to true and false.

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And then, finally,

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make sure that we get the indentation right,

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we're going to append the value.

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So if I click run, I get 'b' and 'n'.

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Again, if you didn't get this right away, don't worry.

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It can get tricky, and this is one of those things

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that you just need to keep practicing.

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But you see here that I was able to use loops.

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I was able to use logical operators, like not,

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and conditionals, like if statements,

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to solve a problem in just a few lines of code.