1 00:00:01,630 --> 00:00:10,200 In this lecture I'll explain one of the most important concepts in Python programming, that is for loops. 2 00:00:10,330 --> 00:00:16,600 I'll use an example, so you not only understand the syntax how to write a for loop, but you'll also understand 3 00:00:16,900 --> 00:00:18,790 why you should use for loops. 4 00:00:18,790 --> 00:00:26,890 Let's say we've got these temperatures for Monday so maybe this was recorded in the morning in midday, 5 00:00:27,490 --> 00:00:28,840 and that in the evening. 6 00:00:29,380 --> 00:00:37,640 So how can we make a program that prints out the rounded values of each of these values like that? 7 00:00:37,660 --> 00:00:39,430 So that would be the expected output. 8 00:00:39,640 --> 00:00:41,140 You can see it down here. 9 00:00:41,340 --> 00:00:48,010 As you'd get 9 because 9.1 rounded up to the whole number will be 9, and then 10 00:00:48,070 --> 00:00:49,620 8.8, 9 again. 11 00:00:49,630 --> 00:00:51,950 And 7.8, 8. 12 00:00:51,970 --> 00:00:53,440 How can we do that? 13 00:00:53,470 --> 00:01:00,310 So we need to find a way to access the items of the list and you know a method already how to 14 00:01:00,310 --> 00:01:04,750 access list items which is using indexes. 15 00:01:05,950 --> 00:01:09,370 So if you want the first one you use zero. 16 00:01:09,970 --> 00:01:19,260 So you want to print out the first item, that however would print out 9.1, you want the rounded 17 00:01:19,270 --> 00:01:27,520 version of nine points one which is maybe you want to look, to have a look at what functions you have 18 00:01:27,880 --> 00:01:28,540 available. 19 00:01:32,990 --> 00:01:33,960 Like that. 20 00:01:33,990 --> 00:01:42,290 So have a quick look here, and you'll be able to find a round. So round which means you want to round 21 00:01:42,350 --> 00:01:51,680 a number, so round 9.1, you get 9, and in our case the number we'd like to round up is this 22 00:01:51,680 --> 00:01:52,400 expression. 23 00:01:52,400 --> 00:02:02,120 So we want to play round here and in parentheses put that expression. 24 00:02:02,120 --> 00:02:05,330 So that's number, 9.1. 25 00:02:05,330 --> 00:02:10,650 So give it a try before rewriting the entire code and that's fine. 26 00:02:10,700 --> 00:02:12,480 Do that again. 27 00:02:12,490 --> 00:02:13,410 Write. 28 00:02:14,060 --> 00:02:21,830 But with 1 and with 2, executes, and you get the expected output, okay, that's fine, it works but what 29 00:02:21,830 --> 00:02:28,630 if you had a big list of 100 items? You'd end up with 100 lines of code. 30 00:02:28,640 --> 00:02:32,920 Well, I can show you how to do that with just two lines of code instead. 31 00:02:33,370 --> 00:02:37,630 This how you do it. You use a for loop for temperature. 32 00:02:37,650 --> 00:02:46,040 Just choose a name for a variable for temperature in. You see how these keywords are highlighted. 33 00:02:46,040 --> 00:02:49,340 So these are actually Python reserved words. 34 00:02:49,490 --> 00:02:50,920 Temperature is just a variable. 35 00:02:50,930 --> 00:02:56,180 That's why it's in black. In Monday temperatures, use a colon. 36 00:02:56,210 --> 00:02:57,550 And what happens after the colon? 37 00:02:57,560 --> 00:02:59,380 I told you in the earlier video. 38 00:02:59,660 --> 00:03:05,760 Well indentation which happens automatically in Visual Studio Code, four spaces. 39 00:03:05,870 --> 00:03:09,290 What do we want to do for each of the temperatures? 40 00:03:09,290 --> 00:03:17,930 Well, we want to print out the round form of temperature. 41 00:03:17,930 --> 00:03:21,310 Just like that, save, execute. 42 00:03:21,390 --> 00:03:22,820 And this is the output. 43 00:03:23,420 --> 00:03:33,680 So in just two lines of code we are able to execute some commands for all the items of an array which 44 00:03:33,680 --> 00:03:37,040 a least in this case, but it can also be a string. 45 00:03:37,190 --> 00:03:44,600 For example for the letter in "hello", print letter. 46 00:03:48,600 --> 00:03:51,280 And hello is printed out there. 47 00:03:52,230 --> 00:03:55,270 And of course you can do whatever you like there, title. 48 00:03:55,320 --> 00:03:59,620 Get the first item which is the letter. 49 00:03:59,640 --> 00:04:03,400 So the letter would be capitalized like that. 50 00:04:03,420 --> 00:04:09,250 So let me go one more time through these two lines to explain them what they mean. 51 00:04:09,360 --> 00:04:13,790 So what the loop does is for temperature in Monday temperatures. 52 00:04:13,830 --> 00:04:15,650 So you are creating a variable. 53 00:04:15,810 --> 00:04:23,580 And what the loop does is it goes through all these items one by one with loops. 54 00:04:23,580 --> 00:04:27,900 So in the first iteration temperature will be equal, 55 00:04:27,900 --> 00:04:31,960 so the variable will be equal to 9.1. 56 00:04:32,100 --> 00:04:39,420 Therefore the round function will round up nine point one and print it out here. 57 00:04:40,230 --> 00:04:45,900 And if there are more lies in here, for example print "Done". 58 00:04:46,650 --> 00:04:54,320 If you do that you see if there is another more line like after 9, this line is executed. 59 00:04:54,380 --> 00:04:56,790 So you get the string "Done" print it out. 60 00:04:56,870 --> 00:05:00,320 If there are more lines those lines will be executed. 61 00:05:00,320 --> 00:05:06,890 If there is no more lines, then the execution goes again on the top of the for loop, and the loop gets the 62 00:05:06,890 --> 00:05:08,120 second item this time. 63 00:05:08,480 --> 00:05:14,890 So temperature this time will be equal to 8.8 and the same thing happens again, rounded it up, 64 00:05:14,900 --> 00:05:16,040 print it out. 65 00:05:16,050 --> 00:05:19,200 "Done" is also printed out, goes to the next line. 66 00:05:19,430 --> 00:05:20,290 7.6. 67 00:05:20,300 --> 00:05:29,460 And so one, and then after 7.6 the loop tries to see if there are more items in this array. 68 00:05:29,720 --> 00:05:37,730 If there are no more items what happens is that this indented block, the execution of this block finishes 69 00:05:37,820 --> 00:05:43,220 and Python goes to the next two lines to execute what's left in the script.