WEBVTT 0 00:00.260 --> 00:06.140 Now, one of the things that you'll start to realize about the Python programming language, especially 1 00:06.140 --> 00:13.400 if you have experience of other programming languages, is that Python is extremely number friendly. 2 00:13.400 --> 00:18.230 It has a lot of built in functions to help us work with numbers. 3 00:18.230 --> 00:27.350 For example, if I had a class of students and I list each of their exam scores inside this giant list, 4 00:27.350 --> 00:32.980 and I wanted to work out, well, what is the total exam score. 5 00:32.980 --> 00:36.850 So what if I added each of these numbers up together, 6 00:36.850 --> 00:38.110 what would I get? 7 00:38.110 --> 00:46.570 Well, Python has something called the sum(), which allows us to put in any iterable data type, including 8 00:46.570 --> 00:47.200 lists. 9 00:47.200 --> 00:50.170 So I can put the student scores into here. 10 00:50.170 --> 00:56.580 And I can set this, let's say, to the total_exam_score. 11 00:57.090 --> 01:04.830 And then if I print this, you'll see that it has added up each of those numbers in the list, and it 12 01:04.830 --> 01:07.050 equals 2068. 13 01:07.140 --> 01:15.750 Now if I wanted to do this manually though, I could because at the end of the day, all that's happened 14 01:15.780 --> 01:22.940 is the Python team, when they developed the programming language they created each of these helpful 15 01:22.940 --> 01:29.810 functions so we could create some ourselves as well, given that we understand how for loops work. 16 01:29.810 --> 01:38.240 So we could say for score in student_scores, colon. 17 01:38.240 --> 01:47.530 And then in the indented block we could say, well, we need to add each of these scores to each other, 18 01:47.530 --> 01:47.800 right? 19 01:47.800 --> 01:50.740 And then we need some sort of variable to keep hold of it. 20 01:50.740 --> 01:56.440 So let's create a variable called sum and set it to start off as equal to 0. 21 01:56.440 --> 02:01.630 And then we could say, sum += score. 22 02:01.630 --> 02:07.540 And every time this for loop runs it's going to go to the next score and the next score, 23 02:07.540 --> 02:15.930 and each time that score is added to the previous value of sum, so then it accumulates in that variable. 24 02:15.960 --> 02:24.990 So now what we can do is go ahead and print the sum and go ahead and hit Run. 25 02:24.990 --> 02:29.700 And you can see that it's exactly the same number as before. 26 02:30.720 --> 02:38.630 So this is a way that we can use the primitive parts of Python. 27 02:38.630 --> 02:47.750 So the building blocks of Python, to build out functionality for various use cases, such as summarizing 28 02:47.750 --> 02:51.560 each of the numbers in a list and adding them together. 29 02:51.770 --> 02:54.470 So here is your challenge. 30 02:54.470 --> 03:00.860 You're going to do the same, but in your case you're going to try and replicate the max functionality. 31 03:00.860 --> 03:09.010 So this is a built-in function that allows us to pass in a list, for example, student_scores, 32 03:09.010 --> 03:17.080 and if we print it, you can see it will pick out the largest number in this list, which happens to 33 03:17.080 --> 03:18.730 be 199. 34 03:18.760 --> 03:27.360 Now your job is to replicate this functionality, but using what you have learned about for loops, 35 03:27.360 --> 03:33.900 about Lists, about Conditionals, and see if you can figure out how to achieve this. 36 03:34.050 --> 03:38.130 So pause the video now and give this challenge a go. 37 03:42.120 --> 03:50.880 So similar to previously, we will use a for loop to loop through each of the scores in the list of 38 03:50.880 --> 03:52.320 student_scores. 39 03:52.340 --> 03:58.250 and if you want to verify it as you go along while you're writing your code, it's always a good idea 40 03:58.250 --> 04:02.960 just to make sure that your code is doing what you expect it to do. 41 04:02.960 --> 04:05.780 So in this case, we're going through each of the scores. 42 04:05.780 --> 04:14.690 Now instead of printing it, we want to check it against the number which we want to set as maximum. 43 04:14.690 --> 04:24.010 So similar to sum we need a variable to hold all of the intermediate values until we reach the maximum. 44 04:24.010 --> 04:32.980 So let's create a variable called max_ score and let's just set it to equal 0. 45 04:33.190 --> 04:41.320 Now when we loop through each of the scores, we're going to compare the current score that the loop 46 04:41.320 --> 04:42.190 is going through. 47 04:42.190 --> 04:45.270 So the first time it will be looking at 150. 48 04:45.270 --> 04:53.580 And we're going to say, well, if the score that we're currently looking at, let's say 150 is greater 49 04:53.580 --> 05:01.890 than the max_score, well, in that case, we're going to set the max_score to this current score that 50 05:01.890 --> 05:03.150 we're looking at. 51 05:03.150 --> 05:08.070 And what this loop is going to do is it's going through each of these numbers. 52 05:08.070 --> 05:12.950 So let's go through the first three in order, just so that we can make this process a bit more clear 53 05:12.950 --> 05:13.790 in your mind. 54 05:13.820 --> 05:16.580 The first score is equal to 150. 55 05:16.580 --> 05:19.220 Is 150 greater than 0? 56 05:19.220 --> 05:20.360 Well, yes. 57 05:20.360 --> 05:23.750 So then this bit of code carries out, 58 05:23.750 --> 05:27.260 and now the max score is equal to 150. 59 05:27.260 --> 05:30.410 So for the next score it's 142. 60 05:30.440 --> 05:33.410 So is 142 greater than 150? 61 05:33.430 --> 05:34.210 No. 62 05:34.210 --> 05:36.550 So we're not going to do anything at all. 63 05:36.550 --> 05:41.770 You could, of course, have an else statement that just prints something, but in this case it's unnecessary. 64 05:41.770 --> 05:48.940 We only need to check for one thing, and that one thing is each time we loop through each of the scores, 65 05:48.940 --> 05:52.660 is it greater than the previous maximum? 66 05:52.750 --> 05:58.150 And now if I go ahead and exit the indentation levels and go to the very start. 67 05:58.150 --> 06:07.770 So I'm outside of the for loop and I print out the max score, you'll see that it will give me the same 68 06:07.770 --> 06:12.960 result as using the max function, which is 199. 69 06:13.110 --> 06:20.160 So if this code doesn't make any sense to you, I recommend going back to the previous lesson and revising 70 06:20.160 --> 06:22.200 what we learned about for loops. 71 06:22.230 --> 06:28.220 Alternatively, maybe you need to do some revision on how if statements and conditionals work, but 72 06:28.220 --> 06:33.740 either way, make sure that all of this code makes perfect sense to you, and you can write it from 73 06:33.740 --> 06:39.380 scratch without having to look at the answer code, because it's really, really important. 74 06:39.380 --> 06:46.130 As we progress that, I'm going to assume that all of this makes sense to you so that we can build upon 75 06:46.130 --> 06:47.180 our knowledge. 76 06:47.180 --> 06:50.360 And then once you're ready, I'll see you over in the next lesson.