1 1 00:00:00,000 --> 00:00:03,250 In this video we're going to code a Blueprint. 2 2 00:00:03,250 --> 00:00:05,050 The first thing to do is to go ahead 3 3 00:00:05,050 --> 00:00:07,640 and create your app.py. 4 4 00:00:07,640 --> 00:00:11,160 And I've also created a new file called learning.py. 5 5 00:00:11,160 --> 00:00:14,000 learning.py will contain our blueprint 6 6 00:00:14,000 --> 00:00:16,883 and app.py will contain our app definition. 7 7 00:00:18,020 --> 00:00:19,760 In app.py we are going to say 8 8 00:00:19,760 --> 00:00:21,893 from flask import Flask, 9 9 00:00:22,900 --> 00:00:24,853 and then we're going to define our app. 10 10 00:00:26,390 --> 00:00:27,910 As usual we're gonna say 11 11 00:00:27,910 --> 00:00:30,800 app is Flask with dunder name, 12 12 00:00:30,800 --> 00:00:33,460 and this is going to define our flask app. 13 13 00:00:33,460 --> 00:00:36,630 Then, whatever we do, we have to define 14 14 00:00:36,630 --> 00:00:39,430 a route for our flask app. 15 15 00:00:39,430 --> 00:00:40,650 So the way we do that is we say 16 16 00:00:40,650 --> 00:00:44,523 app.route and then we define the endpoint, 17 17 00:00:45,510 --> 00:00:47,560 and in this case we're going to leave it as that 18 18 00:00:47,560 --> 00:00:50,970 and then we're gonna say what function 19 19 00:00:50,970 --> 00:00:55,300 is going to run when we access this endpoint 20 20 00:00:55,300 --> 00:00:56,410 and then we're going to go ahead 21 21 00:00:56,410 --> 00:00:58,743 and say something like Hello, world! 22 22 00:00:59,620 --> 00:01:02,520 So obviously a very simple endpoint here. 23 23 00:01:02,520 --> 00:01:03,770 Not much happening, 24 24 00:01:03,770 --> 00:01:06,610 this is just something that we've seen before 25 25 00:01:06,610 --> 00:01:07,810 and then at the end we're gonna say 26 26 00:01:07,810 --> 00:01:09,300 if name equal 27 27 00:01:10,360 --> 00:01:13,303 main, we're gonna say app.run. 28 28 00:01:15,220 --> 00:01:19,110 Alright, so this is the most basic flask app, 29 29 00:01:19,110 --> 00:01:20,950 something we've looked at before. 30 30 00:01:20,950 --> 00:01:22,940 The thing about blueprints is that 31 31 00:01:22,940 --> 00:01:25,160 when your app starts to grow, 32 32 00:01:25,160 --> 00:01:28,280 you have more and more of these endpoints, 33 33 00:01:28,280 --> 00:01:31,147 you don't want them all inside app.py. 34 34 00:01:31,147 --> 00:01:32,450 And the reason for that is 35 35 00:01:32,450 --> 00:01:34,180 that your app.py can get very long, 36 36 00:01:34,180 --> 00:01:35,600 it can get difficult to work with, 37 37 00:01:35,600 --> 00:01:37,240 it can be difficult to find 38 38 00:01:37,240 --> 00:01:38,680 whenever you wanna change something, 39 39 00:01:38,680 --> 00:01:40,600 where that something is. 40 40 00:01:40,600 --> 00:01:43,230 So, a good thing to do in flask apps 41 41 00:01:43,230 --> 00:01:45,380 is to split out of the endpoint, 42 42 00:01:45,380 --> 00:01:47,630 into related endpoints. 43 43 00:01:47,630 --> 00:01:49,140 So, whenever you have a bunch of endpoints 44 44 00:01:49,140 --> 00:01:51,350 that are related to the same thing, 45 45 00:01:51,350 --> 00:01:54,820 you can split them out and put them into a blueprint. 46 46 00:01:54,820 --> 00:01:55,810 So that's what we're gonna do. 47 47 00:01:55,810 --> 00:01:58,150 We're gonna take this endpoint here, 48 48 00:01:58,150 --> 00:02:01,160 and we're going to put it into our learning blueprint, 49 49 00:02:01,160 --> 00:02:03,950 just to show you how blueprints work. 50 50 00:02:03,950 --> 00:02:05,440 So, what I'm gonna do is 51 51 00:02:05,440 --> 00:02:08,200 take this endpoint here, I'm gonna cut it. 52 52 00:02:08,200 --> 00:02:09,800 I'm gonna remove it there, 53 53 00:02:09,800 --> 00:02:12,123 and then I'm gonna go over to learning.py, 54 54 00:02:13,140 --> 00:02:17,030 and I'm going to say from flask import Blueprint. 55 55 00:02:17,030 --> 00:02:19,340 And now we can define our blueprint 56 56 00:02:21,360 --> 00:02:22,890 and give it a name. 57 57 00:02:22,890 --> 00:02:27,880 This name is not going to be terribly useful right now, 58 58 00:02:27,880 --> 00:02:31,630 but we will be using this name later on in the course. 59 59 00:02:31,630 --> 00:02:34,398 And so this name here is how you will be accessing 60 60 00:02:34,398 --> 00:02:36,920 the blueprint's endpoints later on, 61 61 00:02:36,920 --> 00:02:39,170 if you wanna do that dynamically. 62 62 00:02:39,170 --> 00:02:40,170 We will be doing that. 63 63 00:02:40,170 --> 00:02:42,710 Then, we're gonna paste our endpoint here. 64 64 00:02:42,710 --> 00:02:46,210 But now notice how app is not defined. 65 65 00:02:46,210 --> 00:02:48,560 It says unresolved reference app. 66 66 00:02:48,560 --> 00:02:51,870 Of course, we don't have access to the app here. 67 67 00:02:51,870 --> 00:02:54,560 So what we're gonna do is instead of doing app.route, 68 68 00:02:54,560 --> 00:02:57,960 we're gonna say learning_blueprint.route. 69 69 00:02:57,960 --> 00:03:00,830 Now, this route here 70 70 00:03:00,830 --> 00:03:04,500 is defined only inside the blueprint. 71 71 00:03:04,500 --> 00:03:06,100 It is not defined in the app, 72 72 00:03:06,100 --> 00:03:09,550 and the app does not have access to that endpoint. 73 73 00:03:09,550 --> 00:03:11,800 In order to give the app access to that endpoint, 74 74 00:03:11,800 --> 00:03:13,410 we have to import 75 75 00:03:15,100 --> 00:03:16,530 the learning blueprint, 76 76 00:03:16,530 --> 00:03:20,253 and we also have to register the blueprint. 77 77 00:03:23,470 --> 00:03:26,280 So, when we register the blueprint like this, 78 78 00:03:26,280 --> 00:03:29,030 that means that this endpoint here 79 79 00:03:29,030 --> 00:03:34,030 is almost as if it were defined as we had before, app.route. 80 80 00:03:34,380 --> 00:03:37,140 Because we've registered the blueprint onto the app, 81 81 00:03:37,140 --> 00:03:39,700 the app has access to that endpoint, 82 82 00:03:39,700 --> 00:03:42,800 and if we were to run our app and access that endpoint, 83 83 00:03:42,800 --> 00:03:45,080 it would indeed return a hello world. 84 84 00:03:45,080 --> 00:03:46,310 So, we can do that just now. 85 85 00:03:46,310 --> 00:03:50,350 We're gonna go app.py, right click it, and run it. 86 86 00:03:50,350 --> 00:03:52,603 And there you have that. 87 87 00:03:54,160 --> 00:03:55,930 So, now I've brought that window 88 88 00:03:55,930 --> 00:03:56,930 over here to the right, 89 89 00:03:56,930 --> 00:03:59,910 so you can see what happens when you access the endpoint. 90 90 00:03:59,910 --> 00:04:02,440 Notice that we're not accessing any particular endpoint, 91 91 00:04:02,440 --> 00:04:04,990 this is just the home, or the base endpoint, 92 92 00:04:04,990 --> 00:04:08,390 because our blueprint has that defined there. 93 93 00:04:08,390 --> 00:04:11,580 If we wanted to do something like string name, for example, 94 94 00:04:11,580 --> 00:04:15,230 to be able to pass a parameter onto the endpoint, 95 95 00:04:15,230 --> 00:04:18,680 we could do that, and then we can make it return 96 96 00:04:18,680 --> 00:04:19,530 something different. 97 97 00:04:19,530 --> 00:04:23,790 So here, we're gonna refresh the app, and then... 98 98 00:04:23,790 --> 00:04:25,720 Now if we access this, it says not found, 99 99 00:04:25,720 --> 00:04:27,750 of course, and if we say 100 100 00:04:27,750 --> 00:04:30,280 something like Rolf, now we get Hello, Rolf! 101 101 00:04:30,280 --> 00:04:32,280 By the way, new thing here that we've not looked at 102 102 00:04:32,280 --> 00:04:34,690 previously in this course is this f string. 103 103 00:04:34,690 --> 00:04:36,990 You put an f in front of the quotation marks 104 104 00:04:36,990 --> 00:04:38,460 that make up a string, and that means 105 105 00:04:38,460 --> 00:04:40,610 we're creating a formatted string. 106 106 00:04:40,610 --> 00:04:42,500 So then we can use curly braces, 107 107 00:04:42,500 --> 00:04:43,740 and then inside the curly braces, 108 108 00:04:43,740 --> 00:04:45,710 put a variable name. 109 109 00:04:45,710 --> 00:04:48,370 And that's going to replace the variable value 110 110 00:04:48,370 --> 00:04:50,690 into the string, on runtime. 111 111 00:04:50,690 --> 00:04:53,510 So this is going to do hello Rolf. 112 112 00:04:53,510 --> 00:04:56,320 Okay, so now that we have this here, 113 113 00:04:56,320 --> 00:04:57,470 what do we do? 114 114 00:04:57,470 --> 00:05:00,000 Well, we can go over to our app, 115 115 00:05:00,000 --> 00:05:03,450 and notice that as soon as we do slash Rolf, 116 116 00:05:03,450 --> 00:05:05,810 we see hello Rolf. 117 117 00:05:05,810 --> 00:05:07,060 But there are some cases 118 118 00:05:07,060 --> 00:05:11,150 where we want the endpoints related to a specific blueprint 119 119 00:05:11,150 --> 00:05:13,450 to be on their own name space. 120 120 00:05:13,450 --> 00:05:17,100 So, basically, to have their own URL prefix. 121 121 00:05:17,100 --> 00:05:18,093 For example, 122 122 00:05:19,430 --> 00:05:22,793 we could do something like greetings/Rolf. 123 123 00:05:23,730 --> 00:05:24,760 If we do this right now, 124 124 00:05:24,760 --> 00:05:26,270 of course we get not found. 125 125 00:05:26,270 --> 00:05:30,090 But, we can fix that by doing url_prefix=greetings, 126 126 00:05:32,370 --> 00:05:33,780 like that. 127 127 00:05:33,780 --> 00:05:35,575 If we then restart our app, 128 128 00:05:35,575 --> 00:05:37,720 you'll see that this now works. 129 129 00:05:37,720 --> 00:05:39,880 So what we've done is we have said 130 130 00:05:39,880 --> 00:05:43,220 for all the endpoints in this blueprint, 131 131 00:05:43,220 --> 00:05:48,220 just prepend /greetings to the route. 132 132 00:05:48,700 --> 00:05:52,280 So now it would be greetings/string:name. 133 133 00:05:52,280 --> 00:05:53,510 That happens automatically, 134 134 00:05:53,510 --> 00:05:56,920 so we do not have to add the slash greetings in here, 135 135 00:05:56,920 --> 00:05:59,440 and this is particularly useful when you want again 136 136 00:05:59,440 --> 00:06:04,240 all your blueprints to have the same paths at the start. 137 137 00:06:04,240 --> 00:06:06,300 Of course, if we go back to /Rolf, 138 138 00:06:06,300 --> 00:06:08,400 this now is the thing that doesn't work, 139 139 00:06:08,400 --> 00:06:10,860 because it's no longer a valid endpoint. 140 140 00:06:10,860 --> 00:06:12,770 Alright, so that's everything for this video. 141 141 00:06:12,770 --> 00:06:15,370 Wanted to cover blueprints and show you how they work 142 142 00:06:15,370 --> 00:06:16,950 because we're going to be using them 143 143 00:06:16,950 --> 00:06:19,700 pretty extensively in this project. 144 144 00:06:19,700 --> 00:06:20,750 Thanks for joining me. 145 145 00:06:20,750 --> 00:06:22,200 I'll see you on the next one.