WEBVTT 1 00:00:00.250 --> 00:00:01.610 Hi guys and welcome back. 2 00:00:01.610 --> 00:00:03.280 In this video, we're going to talk about how 3 00:00:03.280 --> 00:00:06.070 to add type hinting to our application. 4 00:00:06.070 --> 00:00:07.610 Type hinting is going to be really useful 5 00:00:07.610 --> 00:00:10.510 because it allows to avoid some bugs. 6 00:00:10.510 --> 00:00:12.340 And if you don't know what type hinting is, 7 00:00:12.340 --> 00:00:14.590 we've got a full section dedicated to that 8 00:00:14.590 --> 00:00:16.080 in our complete Python course. 9 00:00:16.080 --> 00:00:17.370 If you're not in that course, 10 00:00:17.370 --> 00:00:18.396 we're gonna leave a couple of links 11 00:00:18.396 --> 00:00:20.560 in the resources section of this lecture 12 00:00:20.560 --> 00:00:21.900 for you to check out instead. 13 00:00:21.900 --> 00:00:22.900 But it's pretty straight forward, 14 00:00:22.900 --> 00:00:23.993 so let's go to it. 15 00:00:25.310 --> 00:00:27.152 Here we've got our application 16 00:00:27.152 --> 00:00:28.140 and what we're gonna do 17 00:00:28.140 --> 00:00:32.230 is we're gonna begin by type hinting our functions here. 18 00:00:32.230 --> 00:00:34.660 So, we're going to go ahead 19 00:00:34.660 --> 00:00:36.643 and add the... 20 00:00:36.643 --> 00:00:37.520 imports. 21 00:00:37.520 --> 00:00:38.730 So from the typing module 22 00:00:38.730 --> 00:00:40.543 we're gonna import list and tuple. 23 00:00:41.980 --> 00:00:44.760 And then we're going to go to down here 24 00:00:44.760 --> 00:00:47.720 where we have get_Poll_details for example. 25 00:00:47.720 --> 00:00:51.540 And every parameter is going to get a type hint. 26 00:00:51.540 --> 00:00:54.110 What that's gonna do is later on when we call this function, 27 00:00:54.110 --> 00:00:57.276 PyCharm is going to know what sort of value 28 00:00:57.276 --> 00:00:59.766 this parameter should be. 29 00:00:59.766 --> 00:01:02.720 So what we're gonna do is Poll_id should be an integer, 30 00:01:02.720 --> 00:01:06.036 so we simply type : int before the bracket 31 00:01:06.036 --> 00:01:10.846 and that annotates the Poll_id and tells the PyCharm linter 32 00:01:10.846 --> 00:01:14.220 or type checker that it should be an integer. 33 00:01:14.220 --> 00:01:15.990 And if we try to call this function with something 34 00:01:15.990 --> 00:01:17.160 that's not an integer, 35 00:01:17.160 --> 00:01:19.006 then PyCharm is gonna give us a warning. 36 00:01:19.006 --> 00:01:21.374 Note that it will be a warning, 37 00:01:21.374 --> 00:01:24.160 and it's never going to be an error. 38 00:01:24.160 --> 00:01:26.260 Type hinting is just a hint, 39 00:01:26.260 --> 00:01:28.265 so that's something to remember. 40 00:01:28.265 --> 00:01:30.485 So the other things that are gonna be integers, 41 00:01:30.485 --> 00:01:32.330 we're gonna annotate as well, 42 00:01:32.330 --> 00:01:35.945 such as this Poll_id down here, Option_id down here. 43 00:01:35.945 --> 00:01:39.350 And for these, there are, for example, strings: 44 00:01:39.350 --> 00:01:43.108 the title and owner, we're going to do str down there. 45 00:01:43.108 --> 00:01:45.370 Options we're going to leave for just now 46 00:01:45.370 --> 00:01:46.335 and we're going to come back to it. 47 00:01:46.335 --> 00:01:48.380 Username is going to be a string 48 00:01:48.380 --> 00:01:51.950 and Option_id is going to be an integer as well. 49 00:01:51.950 --> 00:01:55.950 The Options list here is going to be a list of strings. 50 00:01:55.950 --> 00:01:59.050 So how we annotate that is we use the typing module 51 00:01:59.050 --> 00:02:03.450 and we do list of strings inside square brackets. 52 00:02:03.450 --> 00:02:06.400 That tells the Python type hinting system 53 00:02:06.400 --> 00:02:08.289 that this is going to be a list 54 00:02:08.289 --> 00:02:12.150 and it is going to be a list of strings. 55 00:02:12.150 --> 00:02:14.870 Note that I'm using Python 3.8 at the moment 56 00:02:14.870 --> 00:02:17.490 but, as of Python 3.9, you no longer need 57 00:02:17.490 --> 00:02:19.160 to import the typing module. 58 00:02:19.160 --> 00:02:22.200 You can simply use the built-in list for this. 59 00:02:22.200 --> 00:02:25.340 But, because I'm using Python 3.8, I can't do that yet. 60 00:02:25.340 --> 00:02:28.320 So you do have to import and use the L there 61 00:02:28.320 --> 00:02:31.160 in order to use the list type hinting mechanism 62 00:02:31.160 --> 00:02:33.960 with Python 3.8 and above. 63 00:02:33.960 --> 00:02:35.560 So now that we have got our 64 00:02:35.560 --> 00:02:38.980 parameter type hints for everything, we can also type hint 65 00:02:38.980 --> 00:02:41.913 the return type of these functions, and that is where 66 00:02:41.913 --> 00:02:44.080 it's going to get a bit more interesting. 67 00:02:44.080 --> 00:02:46.110 What I'm going to do is I'm going to 68 00:02:46.110 --> 00:02:48.320 define my own custom types. 69 00:02:48.320 --> 00:02:49.750 And the reason I'm going to do that is because 70 00:02:49.750 --> 00:02:52.030 these are going to reappear everywhere 71 00:02:52.030 --> 00:02:54.870 and I don't want to be duplicating a lot of code. 72 00:02:54.870 --> 00:02:58.120 So I'm going to do Poll is equal to a tuple 73 00:02:58.120 --> 00:03:00.960 of int, string, and string. 74 00:03:00.960 --> 00:03:02.730 And the reason I'm doing this is because 75 00:03:02.730 --> 00:03:05.707 whenever one of my functions is returning a Poll, 76 00:03:05.707 --> 00:03:08.720 that I'm going to signal with the Poll type 77 00:03:08.720 --> 00:03:13.290 and that represents a tuple with three values inside it. 78 00:03:13.290 --> 00:03:14.950 The first one is going to be an integer, 79 00:03:14.950 --> 00:03:16.330 the second one is going to be a string, 80 00:03:16.330 --> 00:03:18.310 and the third one is going to be a string as well. 81 00:03:18.310 --> 00:03:20.410 The reason why I'm doing this is because 82 00:03:20.410 --> 00:03:22.173 the Polls that are coming from my table 83 00:03:22.173 --> 00:03:25.940 are integer, string, and string. 84 00:03:25.940 --> 00:03:27.860 I'm going to do the same for votes. 85 00:03:27.860 --> 00:03:30.510 And the reason I'm not doing it for Option is because 86 00:03:30.510 --> 00:03:32.950 we actually never return Options on their own 87 00:03:32.950 --> 00:03:36.020 right now so we don't need it. 88 00:03:36.020 --> 00:03:39.890 However, we do return Poll with Option joined together. 89 00:03:39.890 --> 00:03:42.560 So I'm going to create a PollWithOption type 90 00:03:42.560 --> 00:03:45.590 that is a tuple that has the Poll: int, str, str; 91 00:03:45.590 --> 00:03:49.130 and that it also has the Option: int, str, int. 92 00:03:49.130 --> 00:03:52.460 So this tuple here represents the joined tables: 93 00:03:52.460 --> 00:03:54.450 the Poll and the Option. 94 00:03:54.450 --> 00:03:55.710 What we do return, though, 95 00:03:55.710 --> 00:03:58.180 are Polls with Options joined together. 96 00:03:58.180 --> 00:04:01.020 So I'm going to create the PollWithOption type here 97 00:04:01.020 --> 00:04:04.940 that is a tuple of Polls: int, str, and str; 98 00:04:04.940 --> 00:04:08.860 joined together with the Option which is int, str, and int. 99 00:04:08.860 --> 00:04:11.760 Note that the Polls have id, title, and owner_username, 100 00:04:11.760 --> 00:04:13.100 so that's these three, 101 00:04:13.100 --> 00:04:15.684 and Options have the id, Option_text, and Poll_id, 102 00:04:15.684 --> 00:04:18.290 so that's these three. 103 00:04:18.290 --> 00:04:20.040 Then we're also going to get PollResults 104 00:04:20.040 --> 00:04:22.140 which is another tuple that we're going to use 105 00:04:22.140 --> 00:04:25.000 and which is an int, str, int, 106 00:04:25.000 --> 00:04:28.080 and a float for the vote percentage. 107 00:04:28.080 --> 00:04:29.960 That's down here. 108 00:04:29.960 --> 00:04:31.860 Now, let's go ahead and use these types 109 00:04:31.860 --> 00:04:35.013 to type hint the return values of our functions. 110 00:04:35.013 --> 00:04:37.975 What we can do, for example here with get_Polls, 111 00:04:37.975 --> 00:04:42.380 is we can do this arrow with a dash and a greater than sign 112 00:04:42.380 --> 00:04:45.170 and then List of Poll, and that is going to 113 00:04:45.170 --> 00:04:47.980 give us the list of tuples that we defined above. 114 00:04:47.980 --> 00:04:49.940 And that means that whenever we get 115 00:04:49.940 --> 00:04:53.517 the values from this function, the caller of the function 116 00:04:53.517 --> 00:04:56.820 will actually be able to see that this is 117 00:04:56.820 --> 00:04:59.123 a list of tuples that are being returned. 118 00:05:00.070 --> 00:05:03.040 PyCharm can make use of that by offering you hints later on, 119 00:05:03.040 --> 00:05:04.710 such as the sort of things that you can do 120 00:05:04.710 --> 00:05:05.890 with a returned value. 121 00:05:05.890 --> 00:05:08.580 For get_latest_Poll, we're going to do 122 00:05:08.580 --> 00:05:10.813 List of PollWithOption. 123 00:05:11.960 --> 00:05:14.990 For Poll details we're going to do the same, actually: 124 00:05:14.990 --> 00:05:16.453 List of PollWithOptions. 125 00:05:17.720 --> 00:05:19.940 For the get_Poll_and_vote_results, we're going to do 126 00:05:19.940 --> 00:05:21.670 a List... 127 00:05:21.670 --> 00:05:23.300 of PollResults. 128 00:05:23.300 --> 00:05:24.640 Note that some of these are lists 129 00:05:24.640 --> 00:05:27.280 even though they only pertain to one Poll, 130 00:05:27.280 --> 00:05:30.823 because the database is returning multiple rows. 131 00:05:32.400 --> 00:05:34.640 This one is simply going to be a Vote 132 00:05:34.640 --> 00:05:38.300 because it gets one random Vote from the database. 133 00:05:38.300 --> 00:05:39.550 And that's about it. 134 00:05:39.550 --> 00:05:42.010 These don't return anything so we can just leave them. 135 00:05:42.010 --> 00:05:44.510 Alternatively, you can always do None, 136 00:05:44.510 --> 00:05:45.530 but it's not necessary. 137 00:05:45.530 --> 00:05:46.870 That's implying that it's just going to add 138 00:05:46.870 --> 00:05:48.313 a bit of craft to your code. 139 00:05:49.560 --> 00:05:52.640 In app.py, there's actually not much typing to do, 140 00:05:52.640 --> 00:05:55.030 or type hinting, because what we've got here 141 00:05:55.030 --> 00:05:57.780 is just this function that actually 142 00:05:57.780 --> 00:05:59.820 accepts anything or returns anything. 143 00:05:59.820 --> 00:06:02.550 And so all we have to do here is go ahead and say 144 00:06:02.550 --> 00:06:04.803 List of database.PollWithOption. 145 00:06:06.200 --> 00:06:08.360 I'm using this here to refer to 146 00:06:08.360 --> 00:06:09.676 the type defined in the database, 147 00:06:09.676 --> 00:06:11.610 because it's just defined in one place. 148 00:06:11.610 --> 00:06:15.170 So I'm not bothered enough to move my types 149 00:06:15.170 --> 00:06:16.400 into a separate file. 150 00:06:16.400 --> 00:06:18.170 You could do that if you are using them 151 00:06:18.170 --> 00:06:20.320 from many different places, but right now 152 00:06:20.320 --> 00:06:21.660 we don't have to do that. 153 00:06:21.660 --> 00:06:23.240 We do have to import this, though. 154 00:06:23.240 --> 00:06:26.700 So I'm going to just click over it and then 155 00:06:26.700 --> 00:06:30.440 find this wee icon, import this name, type in .List, 156 00:06:30.440 --> 00:06:33.010 and that's going to essentially just paste that 157 00:06:33.010 --> 00:06:36.510 up there for me or you could type it yourself, of course. 158 00:06:36.510 --> 00:06:38.010 That's everything for type hinting. 159 00:06:38.010 --> 00:06:39.910 Now what that's going to do is, for example, 160 00:06:39.910 --> 00:06:43.373 if we go down here, and this is going to know that 161 00:06:43.373 --> 00:06:46.250 Poll_with_Options is a tuple. 162 00:06:46.250 --> 00:06:49.367 So if you try to do something like .append(), 163 00:06:50.270 --> 00:06:52.220 then it's going to allow it that. 164 00:06:52.220 --> 00:06:54.010 But if you try to run something here 165 00:06:54.010 --> 00:06:57.070 that doesn't exist in a list, then it's not 166 00:06:57.070 --> 00:06:59.470 going to appear as a suggestion in PyCharm 167 00:06:59.470 --> 00:07:01.067 and it will underline and say, 168 00:07:01.067 --> 00:07:04.290 "List object doesn't have this method," for example. 169 00:07:04.290 --> 00:07:07.090 So it's all pretty good with that. 170 00:07:07.090 --> 00:07:08.440 It's really helpful, especially when 171 00:07:08.440 --> 00:07:11.260 you're doing larger applications. 172 00:07:11.260 --> 00:07:12.380 That's everything for this video. 173 00:07:12.380 --> 00:07:13.630 Thank you guys for watching. 174 00:07:13.630 --> 00:07:15.363 I'll see you in the next one.