WEBVTT 1 00:00:00.450 --> 00:00:01.590 Hi and welcome back. 2 00:00:01.590 --> 00:00:06.030 In this video we're going to talk about property setters. 3 00:00:06.030 --> 00:00:09.460 Let's create a new file that I'm gonna call Flight, 4 00:00:10.640 --> 00:00:13.880 and in here I'm going to just define a simple class 5 00:00:13.880 --> 00:00:17.720 that will be a flight object. 6 00:00:18.560 --> 00:00:19.670 In case you don't know, 7 00:00:19.670 --> 00:00:23.660 flights are normally something that looks like this. 8 00:00:23.660 --> 00:00:26.120 It goes for example from Glasgow 9 00:00:26.120 --> 00:00:27.790 to London Heathrow. 10 00:00:28.700 --> 00:00:30.710 This could be a flight, 11 00:00:31.630 --> 00:00:35.380 and in this flight you have one segment. 12 00:00:35.380 --> 00:00:38.890 A segment is essentially you getting on a plane, 13 00:00:38.890 --> 00:00:41.670 and you landing somewhere else. 14 00:00:41.670 --> 00:00:44.210 If you're going from Glasgow to Toronto, 15 00:00:44.210 --> 00:00:46.910 you'll actually stop in London Heathrow in the middle. 16 00:00:48.830 --> 00:00:50.400 So you'll have something like this, 17 00:00:50.400 --> 00:00:52.590 Glasgow to London Heathrow to Toronto. 18 00:00:54.450 --> 00:00:56.870 So these are two segments. 19 00:00:57.740 --> 00:01:00.780 And the whole thing is known as a flight leg, 20 00:01:00.780 --> 00:01:05.510 so flight leg in this case has two segments. 21 00:01:05.510 --> 00:01:07.400 Glasgow to London Heathrow, 22 00:01:07.400 --> 00:01:09.530 and London Heathrow to Toronto. 23 00:01:10.970 --> 00:01:12.480 Just a bit of background information, 24 00:01:12.480 --> 00:01:14.350 I am sort of getting a bit 25 00:01:16.320 --> 00:01:19.090 disillusioned with the animals and the friend example, 26 00:01:19.090 --> 00:01:21.170 so now that you know a bit more about Python, 27 00:01:21.170 --> 00:01:24.790 I wanted to give you some more interesting examples 28 00:01:24.790 --> 00:01:26.760 of things you can do. 29 00:01:26.760 --> 00:01:29.220 So let's create this flight class. 30 00:01:29.220 --> 00:01:32.000 I'm gonna not repr, 31 00:01:32.000 --> 00:01:34.060 define an init method, 32 00:01:34.060 --> 00:01:36.960 and we're going to get a list of segments. 33 00:01:37.820 --> 00:01:42.500 So this is going to be a list of segment. 34 00:01:42.500 --> 00:01:45.430 Okay, we can import this, of course, 35 00:01:47.210 --> 00:01:49.660 and just import it, 36 00:01:49.660 --> 00:01:53.310 in Python you can press Alt + Enter, if you're on Mac, 37 00:01:53.310 --> 00:01:55.550 or I think it's Control + Enter if you're on Windows 38 00:01:55.550 --> 00:01:57.720 to get that, the type hints, 39 00:01:57.720 --> 00:02:01.270 and then we're just going to say self.segments 40 00:02:01.270 --> 00:02:02.410 equals segments. 41 00:02:03.270 --> 00:02:06.820 Down here we're going to define the class segment, 42 00:02:06.820 --> 00:02:09.730 which is just going to have a departure 43 00:02:09.730 --> 00:02:10.800 and a destination. 44 00:02:19.310 --> 00:02:21.230 Okay, pretty simple class there. 45 00:02:21.230 --> 00:02:24.190 All it does is it has a departure, for example, 46 00:02:24.190 --> 00:02:27.640 GLA, if I can type, 47 00:02:28.570 --> 00:02:31.730 and a destination, let's say London Heathrow, 48 00:02:31.730 --> 00:02:35.560 so that just gets stored in this segment object, 49 00:02:35.560 --> 00:02:38.520 and we're going to get a list of segments passed 50 00:02:38.520 --> 00:02:40.690 over to our flight constructor. 51 00:02:41.730 --> 00:02:45.850 Then, we're going to have something like a property, 52 00:02:45.850 --> 00:02:49.620 that is gonna be a departure point. 53 00:02:51.380 --> 00:02:54.440 So where does this flight begin? 54 00:02:54.440 --> 00:02:56.580 That, it begins 55 00:02:56.580 --> 00:02:59.830 in the first airport of the first segment, 56 00:02:59.830 --> 00:03:01.720 so that's where this flight is gonna begin. 57 00:03:01.720 --> 00:03:06.720 So we're gonna return self.segments[0].departure. 58 00:03:08.310 --> 00:03:10.200 Okay, and it's gonna return a string. 59 00:03:12.380 --> 00:03:14.540 So this is the departure point. 60 00:03:15.440 --> 00:03:20.440 Now if we wanted to overwrite the departure point, 61 00:03:21.860 --> 00:03:24.890 let's say, make the flight depart from 62 00:03:24.890 --> 00:03:26.580 Edinburgh instead of Glasgow, 63 00:03:27.810 --> 00:03:30.480 there is no easy way to do that, 64 00:03:30.480 --> 00:03:34.660 so I'm going to down here write some code to do that. 65 00:03:34.660 --> 00:03:39.660 Okay, I'm gonna say my flight is a flight object there, 66 00:03:39.820 --> 00:03:42.470 that has, let's say a single segment 67 00:03:42.470 --> 00:03:44.690 that goes from Glasgow to London Heathrow, okay, 68 00:03:44.690 --> 00:03:47.420 so now we have a flight object 69 00:03:47.420 --> 00:03:49.010 that has a list of segments, 70 00:03:49.010 --> 00:03:51.310 but it only has one segment in there, 71 00:03:51.310 --> 00:03:55.170 and the segment is going from Glasgow to London Heathrow. 72 00:03:56.290 --> 00:03:58.950 If you print the flight departure point, 73 00:03:58.950 --> 00:04:00.260 notice how it's a property, 74 00:04:00.260 --> 00:04:03.290 so you don't need the method brackets, 75 00:04:03.290 --> 00:04:06.690 you'll get Glasgow, or GLA for Glasgow Airport. 76 00:04:07.610 --> 00:04:11.310 If you then want to make the flight depart from Edinburgh, 77 00:04:11.310 --> 00:04:13.493 you would have to do something like 78 00:04:13.493 --> 00:04:17.800 flight.segments[0].departure equal Edinburgh. 79 00:04:20.460 --> 00:04:22.440 Not terribly simple. 80 00:04:22.440 --> 00:04:27.440 I would rather do flight.departure_point equal Edinburgh. 81 00:04:30.210 --> 00:04:33.680 But of course we know departure point is a method, 82 00:04:33.680 --> 00:04:37.152 so this, can it be done? 83 00:04:37.152 --> 00:04:38.710 Can you do this? 84 00:04:39.770 --> 00:04:41.180 The answer is no, by the way, 85 00:04:41.180 --> 00:04:43.530 you cannot do this right now, 86 00:04:43.530 --> 00:04:46.700 but of course Python knows that you may want to do this, 87 00:04:47.590 --> 00:04:50.980 and it provides you with another decorator you can use. 88 00:04:50.980 --> 00:04:54.780 The decorator is actually quite a magical thing now, 89 00:04:54.780 --> 00:04:58.340 because the decorator will be called departure_point. 90 00:04:59.670 --> 00:05:02.330 So now we use @departure_point which is the name 91 00:05:02.330 --> 00:05:05.980 of our property, .setter, 92 00:05:07.440 --> 00:05:12.440 and then, we can call our method the same thing, 93 00:05:14.120 --> 00:05:16.470 if you want, or you can call it something else, 94 00:05:18.315 --> 00:05:22.140 and of course it needs the value that you're going to 95 00:05:23.860 --> 00:05:27.080 pass in, that's the EDI down there, 96 00:05:27.080 --> 00:05:32.080 and then all we have to say is self.segments[0].departure 97 00:05:32.400 --> 00:05:35.610 equal EDI, okay? 98 00:05:37.360 --> 00:05:39.540 An even better way of doing things, 99 00:05:39.540 --> 00:05:42.710 just because of, sorry, the, 100 00:05:43.920 --> 00:05:45.900 the departure should be equal to val, of course, 101 00:05:45.900 --> 00:05:47.390 not EDI. 102 00:05:47.390 --> 00:05:49.950 An even better way of doing things is the following. 103 00:05:49.950 --> 00:05:53.850 Normally segments are specific flights, 104 00:05:53.850 --> 00:05:55.710 they have specific flight codes, 105 00:05:55.710 --> 00:05:58.350 specific numbers associated with them, 106 00:05:58.350 --> 00:06:00.360 so you can't just say 107 00:06:00.360 --> 00:06:02.970 this flight is now going to depart from Edinburgh. 108 00:06:02.970 --> 00:06:05.340 But what you can do is you can put a different segment 109 00:06:05.340 --> 00:06:07.940 in there altogether, if you want. 110 00:06:07.940 --> 00:06:10.540 So I would rewrite this, so instead of doing this, 111 00:06:11.750 --> 00:06:13.650 just in a professional environment 112 00:06:13.650 --> 00:06:15.770 where your segments cannot change 113 00:06:15.770 --> 00:06:17.660 because they have specific flight codes 114 00:06:17.660 --> 00:06:19.430 associated with them, 115 00:06:19.430 --> 00:06:24.430 I would say the destination is self.segments[0].destination 116 00:06:24.670 --> 00:06:29.590 and then I would say self.segments[0] is a new segment, 117 00:06:29.590 --> 00:06:31.340 where the departure is val, 118 00:06:31.340 --> 00:06:33.730 and the destination is dest, 119 00:06:33.730 --> 00:06:35.760 this thing we calculated up here. 120 00:06:35.760 --> 00:06:38.690 Potentially here you could also, you know, 121 00:06:38.690 --> 00:06:41.890 find out what the flight code is gonna be, 122 00:06:41.890 --> 00:06:45.120 find it in from a database or some other place, 123 00:06:45.120 --> 00:06:47.550 and you know, decide that there. 124 00:06:48.560 --> 00:06:49.660 The only reason I'm doing this 125 00:06:49.660 --> 00:06:50.800 is to show you again 126 00:06:50.800 --> 00:06:53.070 what you could do if you were not able 127 00:06:53.070 --> 00:06:55.060 to change the segments themselves. 128 00:06:55.060 --> 00:06:56.660 You could just create a new one, 129 00:06:56.660 --> 00:06:58.660 replace segments[0] for that, 130 00:06:58.660 --> 00:06:59.610 that would be fine. 131 00:07:01.170 --> 00:07:02.420 Okay? 132 00:07:02.420 --> 00:07:03.790 Now, you can do this. 133 00:07:05.130 --> 00:07:09.260 So you can delete flight.segments[0].departure equal EDI, 134 00:07:09.260 --> 00:07:11.790 and now say flight.departure_point equal EDI. 135 00:07:13.110 --> 00:07:16.220 And if you print flight.departure_point 136 00:07:16.220 --> 00:07:20.690 you'll see when we run flight.py, oh, 137 00:07:23.912 --> 00:07:28.000 yes, sorry, my bad, with the typing, 138 00:07:28.000 --> 00:07:31.670 you have to define this class before the other one, 139 00:07:31.670 --> 00:07:34.250 just the way that Python sees the classes, 140 00:07:34.250 --> 00:07:37.420 it evaluates this method typing, 141 00:07:37.420 --> 00:07:39.180 before it has imported the class, 142 00:07:39.180 --> 00:07:41.040 so you have to define that there, 143 00:07:41.040 --> 00:07:44.380 and then you can see that you can get Glasgow and Edinburgh. 144 00:07:44.380 --> 00:07:48.100 In my notes I actually don't have the typing defined 145 00:07:48.100 --> 00:07:49.050 in the methods, 146 00:07:49.050 --> 00:07:51.470 that's why I didn't realise this before. 147 00:07:52.720 --> 00:07:54.090 So as you can see, 148 00:07:54.090 --> 00:07:58.750 this helps you identify how to change the departure point. 149 00:07:58.750 --> 00:08:00.450 Now you don't even have to know 150 00:08:00.450 --> 00:08:02.400 when you're using the flight object 151 00:08:02.400 --> 00:08:05.030 that this is a property or not. 152 00:08:05.030 --> 00:08:08.150 So whether this is an @property decorated method, 153 00:08:08.150 --> 00:08:10.230 or whether it's an actual property of the flight. 154 00:08:10.230 --> 00:08:13.050 This lets you set them and get them. 155 00:08:15.350 --> 00:08:17.500 Just for completeness as well, 156 00:08:19.290 --> 00:08:23.621 I'm going to define a repr method. 157 00:08:23.621 --> 00:08:26.340 In order to show you how I would do this, 158 00:08:26.340 --> 00:08:28.480 this repr method has to return something, 159 00:08:29.430 --> 00:08:31.010 string in the format 160 00:08:31.870 --> 00:08:36.870 of Glasgow, London Heathrow, Toronto, for example. 161 00:08:39.280 --> 00:08:40.720 So how are you going to do this? 162 00:08:40.720 --> 00:08:44.980 How would you create a string that has this format, 163 00:08:44.980 --> 00:08:47.210 knowing the segments? 164 00:08:47.210 --> 00:08:49.520 I'd encourage you to give this a go, by the way. 165 00:08:49.520 --> 00:08:51.770 line:15% Pause the video and give it a go, if you can. 166 00:08:55.050 --> 00:08:56.350 line:15% Hopefully you tried that. 167 00:08:56.350 --> 00:08:58.090 What I would do is say, 168 00:08:58.090 --> 00:09:00.470 get a list of the stops. 169 00:09:00.470 --> 00:09:02.630 So the first stop of your flight, 170 00:09:02.630 --> 00:09:05.290 or rather where it starts is Glasgow. 171 00:09:05.290 --> 00:09:08.610 The second stop is the end of the first segment, 172 00:09:08.610 --> 00:09:10.510 so you've got the start of the first segment, 173 00:09:10.510 --> 00:09:12.380 end of the first segment. 174 00:09:12.380 --> 00:09:15.060 Then you have the end of the second segment, 175 00:09:15.060 --> 00:09:16.540 and then if it was going somewhere else, 176 00:09:16.540 --> 00:09:19.240 you'd have the end of the third segment, and so forth. 177 00:09:20.080 --> 00:09:22.040 So the stops initially are 178 00:09:23.420 --> 00:09:26.110 self.segments[0].departure, 179 00:09:27.150 --> 00:09:30.210 and self.segment[0].destination, 180 00:09:30.210 --> 00:09:32.710 these are the two initial stops that you know 181 00:09:32.710 --> 00:09:34.150 you're always going to have, 182 00:09:34.150 --> 00:09:36.020 you're always going to have 183 00:09:36.020 --> 00:09:37.550 segments[0].departure, 184 00:09:37.550 --> 00:09:39.360 and segments[0].destination. 185 00:09:40.680 --> 00:09:45.680 Then I would say for seg in self.segments[1] onwards, 186 00:09:47.480 --> 00:09:48.980 stops.append(seg.destination). 187 00:09:51.510 --> 00:09:52.440 Simple enough. 188 00:09:52.440 --> 00:09:55.650 You start then at the first segment, 189 00:09:55.650 --> 00:09:56.930 rather segment number one. 190 00:09:56.930 --> 00:09:59.290 The second segment, if there are any, 191 00:09:59.290 --> 00:10:03.523 and then you append the destination over to your stops, 192 00:10:03.523 --> 00:10:05.000 and at the end you can return 193 00:10:06.840 --> 00:10:07.673 .join(stops). 194 00:10:10.050 --> 00:10:11.410 I'm not sure if we've seen this before. 195 00:10:11.410 --> 00:10:14.040 All this allows you to do is 196 00:10:14.040 --> 00:10:17.810 join each of the elements of the stops list 197 00:10:17.810 --> 00:10:20.270 with this string. 198 00:10:20.270 --> 00:10:22.250 So it will essentially put the first stop 199 00:10:22.250 --> 00:10:23.730 at the start of the string, 200 00:10:23.730 --> 00:10:26.620 the second stop after the string, 201 00:10:26.620 --> 00:10:27.990 and then it will put another string after, 202 00:10:27.990 --> 00:10:30.262 and put the third stop, and so forth. 203 00:10:30.262 --> 00:10:32.960 So essentially creating a string that looks like this. 204 00:10:32.960 --> 00:10:35.160 Now we can just print the flight 205 00:10:35.160 --> 00:10:37.030 instead of printing departure point. 206 00:10:37.030 --> 00:10:38.580 We can run it again, 207 00:10:38.580 --> 00:10:40.170 and we can see that we've now 208 00:10:40.170 --> 00:10:41.830 gone from Glasgow to London Heathrow, 209 00:10:41.830 --> 00:10:43.870 over to Edinburgh to London Heathrow, 210 00:10:43.870 --> 00:10:46.410 and here we've learned about a few things 211 00:10:46.410 --> 00:10:48.250 like the setter, 212 00:10:51.159 --> 00:10:54.700 and also how to use the setter in a property, 213 00:10:54.700 --> 00:10:56.410 and we've got some more practise 214 00:10:56.410 --> 00:11:00.180 at defining some actual, real examples of code. 215 00:11:01.110 --> 00:11:01.943 That's it for this video. 216 00:11:01.943 --> 00:11:03.549 I wanted to show you 217 00:11:03.549 --> 00:11:05.120 how to use the setter in a property. 218 00:11:05.120 --> 00:11:06.458 So thank you for joining me, 219 00:11:06.458 --> 00:11:08.108 and I'll see you on the next one.