WEBVTT 00:04.910 --> 00:06.430 By everyone and welcome back. 00:06.680 --> 00:13.910 So in the last video we saw how the whole web development cycle happens from starting from when you 00:13.910 --> 00:16.640 type your out into your browser. 00:16.790 --> 00:18.980 All the way until you get your response. 00:18.980 --> 00:24.840 So in this video we're going to be basically understanding what these nine lines of code are doing. 00:24.910 --> 00:29.270 And we're going to add a little bit on it just to make sure that we understand everything. 00:29.350 --> 00:29.710 OK. 00:29.780 --> 00:30.820 Let's get started. 00:30.980 --> 00:34.910 So the first line here is we're basically importing the required libraries. 00:34.940 --> 00:36.830 We're always going to import these. 00:37.000 --> 00:41.930 So flask is the name of the package which is basically in a flask framework. 00:42.080 --> 00:48.740 And then we're importing flask the capital F which is the constructor of the flask application. 00:48.950 --> 00:54.740 And then where we're turning the flask application and calling giving the name. 00:54.770 --> 01:01.220 So you can just call it the name which is usually main is fine you can change the name to anything else 01:01.220 --> 01:02.530 that's fine. 01:02.630 --> 01:10.970 So you could also write here you know flask you know hi or whatever but we just it's a convention that 01:10.970 --> 01:14.050 we do underscore or name a French Quarter. 01:14.810 --> 01:19.860 And then here's the thing we do at app dot route slash. 01:20.350 --> 01:22.420 So what does that really mean. 01:22.430 --> 01:25.220 This means that once the server is up and running. 01:25.220 --> 01:33.300 So once we click once we come here and we write flask run once this server is running an application 01:33.320 --> 01:39.580 apt piecewise running then this application is always listening on slash. 01:39.720 --> 01:40.250 OK. 01:40.400 --> 01:43.750 It's always waiting for someone to ride. 01:44.030 --> 01:51.640 So always waiting for someone to write one to seven point zero point zero point one slot 5000. 01:51.680 --> 01:58.690 So the port that we're running on and then and then the port we're running on and then slash. 01:58.730 --> 02:05.990 So once some once they get a request at this slash right this here is basically what's under the IP. 02:05.990 --> 02:14.990 Once get a request and slash that tells flask a flask make this function handle the request and return 02:14.990 --> 02:15.890 the response. 02:15.950 --> 02:16.770 OK. 02:16.790 --> 02:19.190 So let's take let's find another one. 02:19.190 --> 02:23.670 Let's write an app loops app around. 02:24.290 --> 02:27.940 But then this time we're going to do it to slash. 02:28.130 --> 02:29.070 Hi there. 02:29.420 --> 02:30.220 OK. 02:30.710 --> 02:36.170 And then we're going to define another function called high there doesn't have to be the same name so 02:36.220 --> 02:37.620 I can use it. 02:37.970 --> 02:40.480 Hi there everyone. 02:40.660 --> 02:41.500 Okay. 02:41.960 --> 02:51.010 And then I'm going to return something else so returning I just hit slash either. 02:51.650 --> 02:52.260 OK. 02:53.120 --> 02:56.230 And now that means that flacid going to be a list. 02:56.320 --> 03:00.200 Any request that comes at slash and then it returns. 03:00.210 --> 03:07.170 Hello world or it's going to be listening of any request that comes at Hi there and then once it receives 03:07.170 --> 03:13.410 it it produces the response which is the string over a year and returns it to the browser. 03:13.440 --> 03:15.440 The browser that requested it. 03:15.690 --> 03:19.410 So we can go keep doing this you know we can do and around. 03:19.440 --> 03:28.380 And then another one was the slash by and then I'm going to find another function called and then returned 03:28.380 --> 03:29.030 by. 03:29.120 --> 03:29.590 OK. 03:29.790 --> 03:34.940 I can also add do some extra stuff like for example seek or. 03:35.990 --> 03:40.700 Two times 534. 03:41.190 --> 03:50.250 And then we can say s is equal to string C and then we can also return s if you want or whatever but 03:50.340 --> 03:55.680 I'm just going to leave it to you so you can basically do all the hyphen computation that you feel like 03:56.460 --> 03:58.050 in this area over here. 03:58.140 --> 04:06.890 And then once you're done all the competition so what you're doing here is prepare a response for other 04:06.890 --> 04:11.490 request that came to slash line. 04:11.670 --> 04:18.270 So once you're ready with a response you simply refuse the return function and return the string. 04:18.270 --> 04:21.180 Now a couple things to keep in mind right. 04:21.270 --> 04:27.210 The return function here takes either or it can take a couple things. 04:27.300 --> 04:33.550 But mostly we use either a string and this course we're going to be using a string or a Jason and we're 04:33.550 --> 04:40.110 going to go explain what what Jason's are in the videos or I can take also a page. 04:43.020 --> 04:46.590 So basically what this application is going to do. 04:46.620 --> 04:47.620 Let's first. 04:47.850 --> 04:53.890 And then stop this Control-C run the flask application. 04:53.920 --> 04:55.050 Good browser. 04:58.270 --> 05:05.500 And then let's say let's go to one twos seven point zero and a couple things your host here might be 05:05.500 --> 05:06.900 different than mine. 05:07.180 --> 05:07.900 It's fine. 05:07.900 --> 05:13.540 You should if your host machine is going to already install a ritual machine it might be zero. 05:13.600 --> 05:15.570 Zero zero zero is fine. 05:15.700 --> 05:17.160 Don't worry about it for now. 05:17.160 --> 05:19.980 We're going to fix this problem later. 05:20.050 --> 05:28.120 So I'm going to listen at Port 5000 and then I'm going to go to for example let's say only slash. 05:28.150 --> 05:29.940 We'll see what happens I get. 05:30.010 --> 05:30.990 Hello world. 05:31.210 --> 05:34.940 What if I didn't go to slash either. 05:35.320 --> 05:38.120 Well I just hit slash high there. 05:38.140 --> 05:40.580 So I just reached here. 05:40.780 --> 05:44.510 You can see that I got get at slash Heidi. 05:44.530 --> 05:49.650 So I got to request a time here and then this function is now responsible. 05:49.650 --> 05:55.110 Hi there everyone started handling preparing the response for this request. 05:55.180 --> 06:01.830 What if I go to slash by then I get by again. 06:02.050 --> 06:03.350 I did some computation. 06:03.360 --> 06:04.470 If I want to return. 06:04.520 --> 06:10.300 Competition's fine but I don't have to simply return and the response. 06:10.300 --> 06:12.050 Now what's this here. 06:12.070 --> 06:12.960 What's this. 06:13.090 --> 06:19.690 Here it says basically you should be familiar with this these two lines in Python to make sure that 06:19.690 --> 06:22.200 it's actually running from this directory. 06:22.360 --> 06:28.400 But it's fun usually just do it at it's name equal to mean that and they're run. 06:28.450 --> 06:35.770 Now what these two here over here if we take this over here if we take it out and then we save and then 06:35.770 --> 06:36.610 we run it. 06:36.880 --> 06:40.260 OK flask one is going to work perfectly. 06:40.260 --> 06:42.150 No no problems with the problem. 06:42.160 --> 06:45.730 So if you go here again to lie then it replay. 06:45.840 --> 06:48.230 See your question it's fine. 06:48.420 --> 06:49.900 Glasses buy. 06:49.960 --> 06:55.500 So basically what this does is it tells us where the host is. 06:55.540 --> 06:56.800 Where should we run. 06:57.040 --> 07:03.250 And usually we just leave it empty until we actually deploy so we don't have to worry about this area 07:03.250 --> 07:04.240 over here. 07:04.270 --> 07:06.630 Don't forget about it it's not important. 07:06.820 --> 07:13.990 But one of that import more important things to do is to care about debug or trip over while you're 07:13.990 --> 07:14.820 developing this. 07:14.830 --> 07:20.800 This is a very important thing to do because when you do Deeble equal to true then let's say for example 07:20.800 --> 07:27.870 I did something bad here so I say let's see I divide by zero right. 07:27.880 --> 07:36.830 So C equals to 1 divided by zero rights should give me a arithmetic error right and then return by. 07:37.060 --> 07:44.790 So if I say this and then I restart my server and then I go to slash by over here. 07:46.590 --> 07:52.290 I'm going to I'm going to get an internal air here internal server and it's going to tell me lots of 07:52.290 --> 07:53.220 errors here. 07:53.360 --> 07:56.820 So this is important because you want to know what happened wrong. 07:56.820 --> 08:01.860 It says here Zero a division tells me that can't define 0 0. 08:02.040 --> 08:03.060 So this is important. 08:03.060 --> 08:09.360 And also once we fix this host problem you're also going to notice that the this page is not going to 08:09.360 --> 08:15.030 display internal server error is actually going to display this here over here. 08:15.030 --> 08:21.450 This whole traceback is going to be shown over here but for now since we're running on a virtual machine 08:21.450 --> 08:27.270 things are a bit if you were going to get to that later we're going to fix this problem in the coming 08:27.270 --> 08:27.930 videos. 08:27.930 --> 08:34.530 But for now just know that debugging or true is important because it helps us you know once we get an 08:34.530 --> 08:39.790 error it displays the error here and then we can read and understand what's happening like here. 08:39.830 --> 08:42.070 I know ocean divided by zero. 08:42.090 --> 08:43.020 I come here. 08:43.310 --> 08:45.650 You know I come out a winner. 08:45.770 --> 08:49.190 So yeah hopefully this made sense. 08:49.290 --> 08:53.770 Make sure it's running and then I go again to Ratzinger. 08:53.880 --> 08:58.650 So hopefully this made sense. 08:58.650 --> 09:06.780 One last thing that I would like to talk about is what's the difference between a web application and 09:06.780 --> 09:07.920 a web service. 09:07.920 --> 09:17.070 So in return here we're basically returning usually here in the return in webservices we either return 09:17.230 --> 09:23.130 we we most of the time write web webservices API and mostly we return and Jason we're going to be dealing 09:23.130 --> 09:30.360 with a lot of GSM on the other hand for web applications usually return a page or return for example 09:31.050 --> 09:35.070 indexed each team out or they render something. 09:35.070 --> 09:41.800 So in I believe in flask It's called Return render template. 09:42.030 --> 09:47.900 And then you write index stuff inside him out something along that line. 09:48.090 --> 09:54.080 But basically you're returning page here and that's what a web application is you're returning a page. 09:54.210 --> 09:57.740 But in our case we're building an API or web service. 09:57.840 --> 10:01.590 So I only care about GSM we get Jason from the user. 10:01.590 --> 10:09.750 The user gives us some Jason parse his Jason and then we return him some Jason Gay. 10:10.200 --> 10:11.830 So we're gonna see how. 10:11.970 --> 10:17.430 So in this in this function here I could actually you could have actually sent me some stuff so we're 10:17.430 --> 10:23.490 going to see how we can check that the user sent us some stuff some Jason and then have to parse it. 10:23.490 --> 10:27.400 How to read this Jason and then do some computation here. 10:27.450 --> 10:27.780 Right. 10:27.780 --> 10:31.510 Do some math for example and then prepare it Jason. 10:31.590 --> 10:34.390 So Jason might look something like this. 10:34.620 --> 10:38.550 Turn Janie's son is equal to. 10:38.820 --> 10:47.510 And then for example see Field 1 and then ABC. 10:47.670 --> 10:52.160 And we're going to get we're going to get we're going to discuss Jason's in much more details. 10:52.170 --> 10:57.360 But just so that you understand the difference between a web application and 11:01.180 --> 11:05.990 a web application and web service or or or API. 11:06.410 --> 11:11.380 So yeah basically that's it. 11:11.670 --> 11:18.620 We can also return their return Jason here which might not work in Python 3 because we might need this 11:18.630 --> 11:21.210 function called use on the fly. 11:21.360 --> 11:26.660 But in previous Python versions used to work. 11:26.850 --> 11:33.750 So let's let's just just try to make it work here without the Jason F-I function. 11:33.750 --> 11:37.050 If it's if it has changed then it might give us some error. 11:37.380 --> 11:38.040 Let's see 11:41.290 --> 11:43.400 okay so it returns an error. 11:43.400 --> 11:46.390 So it's called dictionary object is not colorable. 11:46.490 --> 11:49.200 OK so we regard that later on. 11:49.830 --> 11:51.210 It also. 11:51.380 --> 11:53.390 Son if I from here. 11:53.740 --> 11:57.080 And then we can return I. 11:57.340 --> 12:00.320 This is just in the head of it. 12:00.320 --> 12:08.190 So we're going to sound ify this dictionary over here and then we rerun it shouldn't give us and years 12:11.310 --> 12:14.340 OK so here will rotate. 12:14.380 --> 12:14.700 OK. 12:14.710 --> 12:19.170 So we got this Jason back and everything's fine. 12:19.340 --> 12:22.640 Dunk just don't care about this for here Free-Net. 12:22.660 --> 12:28.330 We're going to explain it in much more details but yeah basically think of a web application we're always 12:28.330 --> 12:30.250 returning a page. 12:30.400 --> 12:37.020 But in the case of webservices or API we're returning Jason and we're taking in Jason. 12:37.210 --> 12:42.910 So hopefully this makes sense and we'll continue on in the next video. 12:42.940 --> 12:44.690 So on to the next video because it.