1 00:00:05,270 --> 00:00:11,480 Welcome back everyone in this lecture we're going to discuss if elif and L statements let's begin to 2 00:00:11,480 --> 00:00:13,350 learn more about control flow. 3 00:00:13,400 --> 00:00:17,570 We often only want certain code to execute on a particular condition has been met. 4 00:00:17,570 --> 00:00:23,630 For example if my dog is hungry that's some condition then I will feed the dog perform some action or 5 00:00:23,630 --> 00:00:24,690 some line of code. 6 00:00:25,790 --> 00:00:32,670 So to control the flow of logic we're going to be able to some keywords if elif and else control flow 7 00:00:32,670 --> 00:00:38,820 syntax makes use of colons and in the notation otherwise known as whitespace and this indentation system 8 00:00:38,820 --> 00:00:44,030 is crucial to Python and it's what really sets it apart from other programming languages. 9 00:00:44,050 --> 00:00:49,120 So let's go through the examples of what the actual syntax of an IF statement an elephant statement 10 00:00:49,120 --> 00:00:50,340 would look like. 11 00:00:50,380 --> 00:00:54,580 So let's imagine we want to check some condition before executing a block of code. 12 00:00:54,580 --> 00:00:58,930 What we do is we say if and then we have some sort of condition and eventually that's going to be a 13 00:00:58,930 --> 00:00:59,650 boolean value. 14 00:00:59,650 --> 00:01:06,310 So if true if false for example could say if one is less than two or if a user names equal equal to 15 00:01:06,310 --> 00:01:09,240 admin and then we perform or execute some code. 16 00:01:09,250 --> 00:01:13,400 So notice here we have a colon and then some tab indented spaces. 17 00:01:13,480 --> 00:01:19,380 So that's the block code will be executed when we have that condition to be true. 18 00:01:19,390 --> 00:01:21,870 Now we can also have an if else statement. 19 00:01:21,940 --> 00:01:28,260 Basically if some condition is true we execute some code else we execute and do something else. 20 00:01:28,300 --> 00:01:34,050 So let us hear if statements they're going to have some conditional check colon and then some indication 21 00:01:34,090 --> 00:01:38,710 and a block of code else isn't going to have a condition related to it because the else is going to 22 00:01:38,710 --> 00:01:43,650 execute only when everything above it hasn't been true or the condition hasn't been met. 23 00:01:44,890 --> 00:01:49,570 Now if you want to check for multiple conditions then you can say if some condition colon executes some 24 00:01:49,570 --> 00:01:55,320 code Elif basically checking for some other condition do something different and you can stack as many 25 00:01:55,340 --> 00:01:56,470 Ls as you want. 26 00:01:56,560 --> 00:02:00,850 And at the end if none of those conditions are true you can have an else to do something else. 27 00:02:00,850 --> 00:02:07,530 At the very end OK let's explore these concepts in more detail by helping over to the Adam text editor. 28 00:02:07,540 --> 00:02:09,730 OK here I am at the Adam text editor. 29 00:02:09,790 --> 00:02:11,890 I'm going to start with just a simple IF statement. 30 00:02:12,070 --> 00:02:19,610 I will say if one is less than two colon and when to hit enter as long as you've already said this as 31 00:02:19,640 --> 00:02:22,660 the PI file you should see an automatic in the notation. 32 00:02:22,690 --> 00:02:27,480 If not you can always just tab over or have four spaces and then that's the indentation. 33 00:02:27,490 --> 00:02:33,410 So this is how Python is going to differentiate blocks of code from each other it's all based on indentation. 34 00:02:33,460 --> 00:02:39,440 So I say if one is Leston to go ahead and print's Yep. 35 00:02:39,810 --> 00:02:40,810 So that's all I'm going to do. 36 00:02:40,810 --> 00:02:43,030 Just a simple IF statement let's run this code. 37 00:02:44,660 --> 00:02:45,350 And I see. 38 00:02:45,410 --> 00:02:46,110 Yep. 39 00:02:46,150 --> 00:02:50,000 Now let's see what happens when I switch this to some statement that I know isn't true. 40 00:02:50,000 --> 00:02:53,330 So I'll say if one equals equals to print Yes. 41 00:02:54,590 --> 00:02:59,090 And now I don't see anything printed out which makes sense because one is not equal to two. 42 00:02:59,390 --> 00:03:04,380 So a more realistic example of something we would use this for is maybe that user name check again. 43 00:03:04,380 --> 00:03:12,730 So say user name provided was admen and then we'll have some check equal to admen. 44 00:03:12,990 --> 00:03:24,800 And then I can say if the user name is equal to the check then I can Prince access granted. 45 00:03:24,970 --> 00:03:29,470 So this kind of the examples we're going to be doing throughout the course this sort of boolean checks 46 00:03:29,590 --> 00:03:32,230 a member we can always add in logical operators as well. 47 00:03:32,230 --> 00:03:39,350 So I can say if user name is equal to check and let's say one is equal to 1. 48 00:03:39,620 --> 00:03:41,630 So then we should see Access Granted there. 49 00:03:41,780 --> 00:03:43,460 OK that's a simple IF statement. 50 00:03:43,610 --> 00:03:48,170 Let's imagine that we want to have some sort of backup lock up code in case this wasn't true. 51 00:03:48,170 --> 00:03:55,780 Well what it could then add onto is say else colon and then something else I could say print all above 52 00:03:55,790 --> 00:03:58,750 conditions were not true. 53 00:04:02,590 --> 00:04:05,590 So when I run this right now what would I expect to see. 54 00:04:05,680 --> 00:04:07,470 Currently these conditions are true. 55 00:04:07,510 --> 00:04:09,640 So I should still see access granted. 56 00:04:10,000 --> 00:04:15,040 So I hit enter and I see Access Granted but let's simplify this if statement to something that's just 57 00:04:15,040 --> 00:04:16,390 not going to be true. 58 00:04:16,420 --> 00:04:20,050 So say if one is equal to two. 59 00:04:20,500 --> 00:04:21,550 Well that's definitely not true. 60 00:04:21,550 --> 00:04:24,290 So basically this block of code won't be executed then. 61 00:04:24,430 --> 00:04:25,750 So I'll check this condition. 62 00:04:25,750 --> 00:04:27,220 That's not true it's a false. 63 00:04:27,250 --> 00:04:28,360 So it doesn't execute this. 64 00:04:28,390 --> 00:04:30,050 Instead it drops down to else. 65 00:04:30,100 --> 00:04:33,710 And notice how the indentation if and else are lined up exactly. 66 00:04:33,940 --> 00:04:38,000 That's how Python knows that these two are go together for each other. 67 00:04:38,020 --> 00:04:41,050 So when I run this now I should see all above. 68 00:04:41,050 --> 00:04:42,820 Conditions were not true. 69 00:04:43,210 --> 00:04:46,720 So I'm going to say Python my example about pi enter. 70 00:04:46,750 --> 00:04:49,240 Now I see all the above conditions were not true. 71 00:04:49,240 --> 00:04:52,950 So checking for one condition and then saying else execute another. 72 00:04:53,140 --> 00:04:59,030 However we can always add more conditions to check so we can do this just by tacking on an Ellis statement. 73 00:04:59,140 --> 00:05:00,630 And these are going to have other conditions. 74 00:05:00,640 --> 00:05:01,930 So let's do another one like. 75 00:05:01,960 --> 00:05:04,120 One is equal to 1. 76 00:05:04,230 --> 00:05:14,080 So I can print middle condition true save that and when I run this now I get to see middle condition 77 00:05:14,080 --> 00:05:15,300 is true. 78 00:05:15,310 --> 00:05:17,470 Now if this happens to be false as well. 79 00:05:17,470 --> 00:05:18,750 So now I have this one is false. 80 00:05:18,760 --> 00:05:20,290 This one's false than the else. 81 00:05:20,320 --> 00:05:24,490 At the very end is going to be executed and you can stack as many lives as you want. 82 00:05:24,490 --> 00:05:28,790 So if you want another LFA there maybe can check for fours equal to four. 83 00:05:29,060 --> 00:05:37,230 Prince third condition and now we run this I get back third condition. 84 00:05:37,360 --> 00:05:41,120 Something to keep in mind is let's imagine we have two cases that are true. 85 00:05:41,410 --> 00:05:44,160 So notice right now my second case one is equal to one. 86 00:05:44,170 --> 00:05:46,770 So the condition is true and therefore is equal to four. 87 00:05:46,780 --> 00:05:47,870 That's also true. 88 00:05:47,980 --> 00:05:48,940 When I run this. 89 00:05:48,970 --> 00:05:51,230 So make sure you save that. 90 00:05:51,440 --> 00:05:53,540 I only see middle condition is true. 91 00:05:53,540 --> 00:05:55,310 I don't see this third condition. 92 00:05:55,340 --> 00:05:59,130 That's because it's only going to execute the first hit of a true condition. 93 00:05:59,150 --> 00:06:01,690 It's not going to go down and continue for the rest. 94 00:06:01,690 --> 00:06:07,010 So for if statements and if elif statements and if else statements it's only going to execute the first 95 00:06:07,010 --> 00:06:10,700 block of code that's within a true conditional statement. 96 00:06:10,700 --> 00:06:16,500 All right so let's finish this off by kind of showing one last more realistic example. 97 00:06:16,560 --> 00:06:25,680 So it will do the following we'll say user name is equal to admen will say permission is equal. 98 00:06:25,700 --> 00:06:28,560 True and that's actually all we'll do. 99 00:06:28,600 --> 00:06:44,620 And we'll say if the user name is equal to admen and we have permission then Prince full access health. 100 00:06:44,720 --> 00:06:51,840 So Aliff Well we've got to put a condition there will say a user name is equal to Addleman. 101 00:06:51,880 --> 00:06:53,100 However there's no permission. 102 00:06:53,110 --> 00:07:09,070 So say an's permission is false then old prince admin access only no full permission. 103 00:07:11,960 --> 00:07:22,260 And then else we'll say Prince no access OK so here what we're saying is we have a username admen permission 104 00:07:22,260 --> 00:07:23,510 is equal to true. 105 00:07:23,530 --> 00:07:24,720 So take a look at this. 106 00:07:24,730 --> 00:07:28,020 Try to freeze frame it and see which one do you think is going to execute. 107 00:07:28,030 --> 00:07:31,960 Full access admin access only or no access. 108 00:07:31,970 --> 00:07:35,050 OK so if we take a look at this user name is equal to admin. 109 00:07:35,200 --> 00:07:37,830 So this condition is true and permission is true. 110 00:07:37,840 --> 00:07:40,740 So it looks like we should see right away for access. 111 00:07:40,750 --> 00:07:42,280 So when I run this that's what I see. 112 00:07:42,280 --> 00:07:46,910 Full access no change is permission to be false. 113 00:07:46,930 --> 00:07:51,050 So now when I run this well I'm not going to have permission is equal to true anymore. 114 00:07:51,060 --> 00:07:53,030 Instead it's going to be equal to false. 115 00:07:53,110 --> 00:07:56,740 So I should see adamant access only no full permission. 116 00:07:56,950 --> 00:07:59,020 And now let's set permission. 117 00:07:59,050 --> 00:08:01,800 True but let's go ahead and provide a different username. 118 00:08:01,960 --> 00:08:08,620 We provide Jose as a user name and when I run this I get back no access because none of these conditions 119 00:08:08,620 --> 00:08:10,350 or else were met. 120 00:08:10,780 --> 00:08:12,290 OK that's the very basics. 121 00:08:12,340 --> 00:08:18,040 If elephant statements will be using these a lot for control flow if you have any questions feel free 122 00:08:18,040 --> 00:08:19,560 to post the Q&A forums. 123 00:08:19,690 --> 00:08:20,880 We'll see you at the next lecture. 124 00:08:20,890 --> 00:08:22,210 Well we begin to discuss Lupe's.