WEBVTT 0 00:00.110 --> 00:04.670 Now, up to this point you've seen us use if statements, 1 00:04.700 --> 00:10.730 else statements, elif statements, multiple if statements as well as nested if statements, 2 00:10.730 --> 00:19.340 but the thing that we haven't been able to do thus far is to check for multiple conditions in the same 3 00:19.340 --> 00:20.600 line of code. 4 00:21.020 --> 00:28.310 So how would we be able to combine different conditions and say, well, is the pizza large, and the 5 00:28.310 --> 00:33.770 user wants pepperoni, and extra cheese all in the same line of code. 6 00:33.830 --> 00:38.030 Well, to do this, we would need to learn about the logical operators. 7 00:38.030 --> 00:42.380 So there's three of them that are really useful: "and", "or", and "not". 8 00:42.920 --> 00:44.990 So let's take a look at the first one. 9 00:44.990 --> 00:52.190 When you combine two different conditions using an and operator they both have to be True both A and 10 00:52.190 --> 00:55.580 B for the entire line of code to be True. 11 00:56.060 --> 01:02.390 If just one of them is True, say A is True and B is False, or A is False and B is True, then the 12 01:02.390 --> 01:04.940 overall thing evaluates to False. 13 01:05.570 --> 01:08.990 Now let's try out some of that in actual code. 14 01:08.990 --> 01:14.600 So let's go ahead and go into the Python Console that we see, right here. 15 01:14.600 --> 01:18.740 And here we can write Python code from scratch, 16 01:18.740 --> 01:24.170 so completely independent of everything else and independent of our code files. 17 01:24.170 --> 01:26.780 So let's test out some Python code in here. 18 01:26.780 --> 01:30.470 Let's say that, a = 12. 19 01:30.470 --> 01:38.630 Right? Now, let's say that I wanted to check whether if is a > 15? 20 01:38.990 --> 01:41.030 Well, that is going to be False. 21 01:41.030 --> 01:45.530 Now what about is a > 10? 22 01:45.560 --> 01:46.910 Well, that's going to be True. 23 01:46.940 --> 01:57.950 Now, if I combined this using an "and" statement, I could say, well, is a > 10 and a < 13 24 01:57.950 --> 02:07.400 and hit Enter, then I would get, True, because both a is greater than ten and a is less 25 02:07.400 --> 02:09.020 than 13 are True. 26 02:09.050 --> 02:15.890 So in this case, when both conditions are true, then this entire line gets evaluated to True. 27 02:15.920 --> 02:19.400 But see what happens when just one of them is False. 28 02:19.400 --> 02:24.620 So is a > 15 and a < 13, 29 02:25.280 --> 02:29.030 a is greater than 15 is False, a is less than 13 is True, 30 02:29.030 --> 02:31.010 and now we get False 31 02:31.010 --> 02:31.460 . 32 02:31.610 --> 02:35.990 So that's what happens when you combine different conditions using and. 33 02:36.500 --> 02:41.780 So using the "and" logical operator it looks at two conditions, 34 02:41.780 --> 02:44.240 and to see if they are both True. 35 02:44.240 --> 02:49.010 And if they are both True it becomes True as the final outcome. 36 02:49.010 --> 02:54.830 But if either of these are False, so False and True becomes False. 37 02:54.830 --> 02:58.610 True and False also becomes False. 38 02:58.700 --> 03:03.020 And this is how the and logical operator works. 39 03:03.020 --> 03:10.010 Now if you only needed one of the conditions to be True, then you could use the "or" operator instead. 40 03:10.010 --> 03:17.450 So if C or D were True, or if they're both True, then it will evaluate to True. 41 03:17.870 --> 03:24.740 It's only when both C and D are False, does this statement actually become False. 42 03:25.370 --> 03:28.910 Now the final one is the "not" operator. 43 03:28.910 --> 03:33.500 And all that this does is it basically reverses a condition. 44 03:33.500 --> 03:36.680 So if the condition is False, then it becomes True. 45 03:36.680 --> 03:39.110 If it's True, then it becomes False. 46 03:40.070 --> 03:47.150 So coming back to our code, we can refresh and restart the Python Console and start with the same a = 12 47 03:47.150 --> 03:47.900 . 48 03:47.900 --> 03:54.860 And we can use the or statement by saying, well, is a > 10. 49 03:54.860 --> 03:55.940 That's True, 50 03:56.180 --> 04:02.420 or is a < 10, which is not True. 51 04:02.420 --> 04:07.400 So here we have a condition that is True and a condition that's not True, 52 04:07.400 --> 04:13.130 but because this time instead of using an and, we have an or, between these two conditions, then this 53 04:13.130 --> 04:15.110 will actually evaluate to True. 54 04:15.140 --> 04:22.340 So in this case, using the or True or True will become True. 55 04:22.430 --> 04:26.090 True or False will become True. 56 04:26.090 --> 04:34.790 False or True becomes true and it's only False or False when both of the conditions are False does it 57 04:34.790 --> 04:36.320 actually evaluate to False. 58 04:36.320 --> 04:39.260 So this is quite different from the "and" operator. 59 04:39.290 --> 04:47.840 Now finally with the "not" operator, it only works when the condition that's being checked is False. 60 04:47.840 --> 04:52.550 So effectively it flips the True to the False and False to True. 61 04:52.580 --> 04:53.960 Let me show you what I mean. 62 04:53.960 --> 05:00.470 So we know that a is 12, so is a < 0? 63 05:00.470 --> 05:01.940 Well it's not because it's 12. 64 05:01.940 --> 05:03.590 It's definitely not less than zero. 65 05:03.590 --> 05:08.120 But by putting the not in front of it, it reverses the condition. 66 05:08.120 --> 05:10.010 So a < 0, 67 05:10.040 --> 05:14.870 this will evaluate to False, but putting the not in front of it it becomes True. 68 05:14.870 --> 05:20.660 So not False is True, and not True is False. 69 05:20.690 --> 05:26.990 Coming back to our roller coaster ticketing, let's say that the roller coaster company decided that 70 05:26.990 --> 05:32.060 for everybody who is having a midlife crisis, they would give them free tickets. 71 05:32.060 --> 05:39.500 And according to Wikipedia, midlife crises typically occur when you are 45 to 55 years old. 72 05:39.800 --> 05:43.940 Let's see if we can incorporate this into our code. 73 05:44.000 --> 05:51.650 So let's say that in addition to these existing price categories, what if you had to add a separate 74 05:51.650 --> 05:59.930 price category for those people who are aged between 45 and 55, and those people get to ride for free? 75 06:00.800 --> 06:05.960 Do you think you would be able to change the code using what you've learned about logical operators, 76 06:05.960 --> 06:09.680 in order to incorporate this addition to our program? 77 06:09.830 --> 06:11.720 Pause the video and give that a go. 78 06:15.080 --> 06:18.470 So we've currently got three conditions: 79 06:18.710 --> 06:20.300 age less than 12, 80 06:20.330 --> 06:22.640 age between 12 and 18, 81 06:22.640 --> 06:24.710 and finally everybody else. 82 06:24.740 --> 06:32.240 Now instead of just finishing up there, let's go ahead and add another elif. 83 06:32.240 --> 06:35.270 And here we're going to combine two conditions. 84 06:35.270 --> 06:47.510 We're going to say if the age >= 45 and age <= 55, 85 06:47.540 --> 06:51.110 then we get to catch that midlife crisis window. 86 06:51.890 --> 06:57.650 Well, in this case, we're going to print something like...we're going to say everything's going to be 87 06:57.650 --> 07:00.080 okay, have a free ride on us. 88 07:01.580 --> 07:10.370 And in fact, we don't need to modify the bill in any way because we know that with if, elif, and else 89 07:10.370 --> 07:19.640 statements is that once this condition matches, then everything that's inside this block. 90 07:19.640 --> 07:25.880 So everything that's indented inside this elif is going to be carried out, namely printing this out, 91 07:25.880 --> 07:33.140 and then it's going to skip the rest of this if else block and continue on. 92 07:33.800 --> 07:39.260 Now, if they want a photo, they still have to pay $3, but at least their ticket is free. 93 07:39.260 --> 07:44.690 And we've been able to do this because we know about the "and" logical operator. 94 07:45.410 --> 07:52.460 Now, for the keen eyed amongst you, you might have noticed with this condition check, we have a warning 95 07:52.460 --> 07:53.630 underneath it. 96 07:53.750 --> 08:01.460 And this says that there's actually a simpler way of writing this expression, and it tells us that 97 08:01.460 --> 08:10.760 we can actually simplify it. Now because we're checking two conditions and we have the "and" logical operator 98 08:10.760 --> 08:11.750 in between, 99 08:11.750 --> 08:15.860 sometimes you might want to make this code less wordy. 100 08:15.860 --> 08:22.910 So if you hover over this warning and you click on Simplified chained comparison, it will give you a 101 08:22.910 --> 08:31.430 simpler way of doing this comparison using two of these checks, either side of the age, 102 08:31.430 --> 08:36.440 and it does exactly the same thing, but in less words of code. 103 08:36.440 --> 08:46.490 But here is the big but, looking at this, is this easier to understand and logic through versus this? 104 08:46.490 --> 08:53.330 Because to somebody who's just starting Python programming, I think this is easier to understand 105 08:53.330 --> 08:56.840 what's going on. Is age greater or equal to 45, 106 08:56.840 --> 09:00.290 and is age less than or equal to 55? 107 09:00.920 --> 09:07.310 So even though there is this warning in here, I'm going to leave it in this format because a lot of 108 09:07.310 --> 09:13.100 you are just starting out learning how to code, and this is a much easier way of reasoning about what's 109 09:13.100 --> 09:15.140 going on in this line of code. 110 09:15.140 --> 09:20.810 So the thing with warnings are that they're really helpful once you get going as a programmer, 111 09:20.810 --> 09:25.130 but in the learning stage, I wouldn't worry too much about all of it. 112 09:25.130 --> 09:30.470 Look at it, read it, see if you understand what it's trying to tell you, and then you decide which 113 09:30.470 --> 09:32.120 version you prefer.