1 00:00:04,660 --> 00:00:10,580 Alright so before we finish with conditions, I want to look now at in and not in. 2 00:00:10,580 --> 00:00:13,850 There are two uses of in and we're going to be seeing it used with a for 3 00:00:13,850 --> 00:00:18,650 loop later. Here though, we're concentrating on using in as a condition. So we need a 4 00:00:18,650 --> 00:00:22,820 new Python file for this one and I'm still on the same project. I'm going to call 5 00:00:33,280 --> 00:00:36,530 So in is used in sequences and we'll make much more use of 6 00:00:36,530 --> 00:00:40,640 it when we come to look at lists in a later section in the course. One sequence 7 00:00:40,640 --> 00:00:44,510 that we have used, though, is a string - a sequence of characters. So let's type in 8 00:00:44,510 --> 00:00:56,500 some code: parrot is equal to Norwegian Blue. Line 3, letter equals input 9 00:00:56,500 --> 00:01:04,800 parenthesis double quotes enter a character colon and a space there. 10 00:01:04,800 --> 00:01:15,340 Line 5, if letter in parrot colon print parenthesis double quotes, left and right 11 00:01:15,340 --> 00:01:22,180 curly braces in the double quotes, is in, left and right curly braces double quote 12 00:01:22,180 --> 00:01:28,700 dot format parentheses letter comma parrot and two right parentheses. 13 00:01:28,700 --> 00:01:34,640 Then on the next line else colon. On the line after that print parenthesis and in 14 00:01:34,640 --> 00:01:39,140 double quotes, I don't need that letter. 15 00:01:41,840 --> 00:01:46,960 So we'll run that program. I'm gonna start by entering the letter a when asked for 16 00:01:46,969 --> 00:01:53,990 a character here - a is in Norwegian Blue. So that assigns the name letter to a string 17 00:01:53,990 --> 00:01:58,600 value a and line 5 checks if the letter appeared in the parrot string. 18 00:01:58,600 --> 00:02:02,840 a does appear in Norwegian blue so their condition evaluates to true, and we get 19 00:02:02,840 --> 00:02:06,920 the message a is in Norwegian Blue printed out, as you can see. So we're going to run 20 00:02:06,920 --> 00:02:10,880 the program again. This time I'm going to try a letter that doesn't appear in the 21 00:02:10,880 --> 00:02:17,000 string, so I'm going to enter a z. I don't need that letter, is output. 22 00:02:17,000 --> 00:02:21,020 When you enter the input remember that string comparisons are case-sensitive. 23 00:02:21,020 --> 00:02:25,420 If you enter a capital A it won't be found in the string, and you can also check for 24 00:02:25,420 --> 00:02:31,240 longer sequences. So if we run the program again now, I'm going to enter 25 00:02:31,240 --> 00:02:38,260 blue with a capital B and press Enter. Blue is in Norwegian blue. 26 00:02:38,260 --> 00:02:43,940 If you try that with blue all in lowercase it won't be found, and I'll just confirm that, 27 00:02:45,720 --> 00:02:51,400 showing indeed that in is case-sensitive. Alright, so as well as checking if 28 00:02:51,400 --> 00:02:56,600 something is in a sequence we can test if it isn't, and we do that using not in. 29 00:02:56,600 --> 00:03:07,360 So we're going to create a new Python file here and we'll call it notin. 30 00:03:07,360 --> 00:03:14,680 Start by typing activity is equal to, then in double quote input parenthesis and in 31 00:03:14,680 --> 00:03:22,900 double quotes, What would you like to do today? A space there before the double 32 00:03:22,900 --> 00:03:28,090 quote and then the right parenthesis. Then on line 3, if and in double quotes 33 00:03:28,090 --> 00:03:41,060 cinema in lowercase not in activity : print But I want to go to the cinema 34 00:03:41,060 --> 00:03:47,580 and then the double quote and the right parenthesis. If you run this program now, 35 00:03:47,820 --> 00:03:53,020 and I'm going to type I want to learn Python. 36 00:03:54,900 --> 00:03:58,680 We get the output, But I want to go to the cinema. Because the string cinema 37 00:03:58,680 --> 00:04:02,860 isn't in I want to learn Python, the boolean expression evaluates to true. 38 00:04:02,860 --> 00:04:08,050 Remember that we're using not in here. So I've mentioned a few times now, that string 39 00:04:08,050 --> 00:04:13,660 comparisons are case sensitive and this can cause confusion for our users if we 40 00:04:13,660 --> 00:04:19,440 don't handle it correctly. To see what I mean I'm going to run the program again, 41 00:04:19,440 --> 00:04:24,680 and I'm going to enter the text I want to go to the cinema, but I'm going to use a 42 00:04:24,680 --> 00:04:29,300 capital C for cinema, and we still get the message But I want to go to the cinema. 43 00:04:29,300 --> 00:04:32,980 Now that's a bit confusing, or could be, for users of your programs. 44 00:04:32,980 --> 00:04:35,780 Fortunately though, that's an easy thing to deal with. 45 00:04:35,780 --> 00:04:39,220 Python strings have a load of useful functions and one of them converts a 46 00:04:39,220 --> 00:04:44,100 string to lowercase. In fact there are two functions that do a similar thing. 47 00:04:44,100 --> 00:04:49,100 I'll show you how to find them all in a moment but firstly, though, let's modify our program slightly. 48 00:04:49,100 --> 00:04:51,640 And what I'm going to do is, where it's got not in activity after 49 00:04:51,640 --> 00:04:57,260 activity, I'm going to put .casefold. 50 00:04:57,260 --> 00:05:01,880 So the casefold function converts a string to lowercase, but it handles 51 00:05:01,880 --> 00:05:05,420 different character sets better than just converting to lower case would. 52 00:05:05,420 --> 00:05:08,920 Unless you're familiar with languages like German, they have different lowercase 53 00:05:08,920 --> 00:05:12,960 representations of some letters, you probably wouldn't be aware of the problem. 54 00:05:12,960 --> 00:05:16,200 But don't worry, just remember to use casefold rather than lower case 55 00:05:16,200 --> 00:05:21,460 when you want to compare strings. Alrighty, so if I run the code again now, 56 00:05:21,460 --> 00:05:25,960 and this time we're going to type the same thing in, I want to go to the cinema, 57 00:05:25,960 --> 00:05:30,760 with a capital C again. We don't get that confusing message anymore because the 58 00:05:30,760 --> 00:05:35,200 match has now clearly worked using casefold. Alright so I'm going to finish this 59 00:05:35,200 --> 00:05:39,680 video by having a look at all the functions that the Python string class provides. 60 00:05:39,680 --> 00:05:43,690 Let's open a browser and I'll paste in the link, and this link is in the 61 00:05:43,690 --> 00:05:47,980 resources section of this video. Alright, so you can scroll down to the string method 62 00:05:47,980 --> 00:05:51,970 section, or what we can do here to save a bit of time, we can just do a search. 63 00:05:51,970 --> 00:05:56,140 I'm gonna search for string methods. There's string methods. I can just click on this, 64 00:05:56,140 --> 00:06:02,620 well it's just down here anyway. So I'll close down my search. You can see them on screen. 65 00:06:02,620 --> 00:06:06,360 So this is an alphabetical list of all the methods that the string class provides. 66 00:06:06,360 --> 00:06:09,760 You can see there that casefold is the second one there, and you 67 00:06:09,760 --> 00:06:13,090 can read a description there of what it actually does. Now I wouldn't suggest 68 00:06:13,090 --> 00:06:16,600 trying to memorize all these methods but it is worth spending some time reading 69 00:06:16,600 --> 00:06:20,470 about them. When you need to do something such as checking if a string contains 70 00:06:20,470 --> 00:06:24,800 only digits, for example, you'll remember that there's a method to do that. 71 00:06:24,800 --> 00:06:28,020 You won't remember what it's called unless you've used it a few times, but you'll 72 00:06:28,030 --> 00:06:31,420 know where to go to find it. We'll be using quite a few of these methods 73 00:06:31,420 --> 00:06:34,840 through the course so you'll get a lot of practice at using them. 74 00:06:34,840 --> 00:06:38,880 Alright, so we've covered quite a bit about if statements and conditions. Before we move 75 00:06:38,890 --> 00:06:42,520 on to start looking at loops, the next video is going to be a challenge to let 76 00:06:42,520 --> 00:06:47,880 you practice some of what you've learnt so far. See you in the next video.