WEBVTT 00:05.050 --> 00:06.010 Everyone. 00:06.190 --> 00:12.760 So in this video before we started explaining anything in flask or any any of these web applications 00:14.350 --> 00:18.850 tools basically we need to really understand what's happening in the web. 00:18.850 --> 00:19.500 Right. 00:19.540 --> 00:24.570 Because if you don't understand what's happening how what happens for example when you write your ad 00:24.640 --> 00:30.020 in your browser and you click enter then you're not you're not going to be able to build a web service 00:30.080 --> 00:34.720 because it all depends on the understanding of the whole entire process. 00:34.720 --> 00:36.000 OK so let's start. 00:36.160 --> 00:38.680 Let's suppose that this is your browser. 00:38.680 --> 00:39.090 OK. 00:39.160 --> 00:41.240 So this is your browser over here. 00:41.350 --> 00:46.740 So your browser and this is the area where you put in your show. 00:46.780 --> 00:54.190 So you're right you know I mean dot Google dot com and you click enter. 00:54.430 --> 00:57.920 So what's the first step that happens when you click enter. 00:58.180 --> 01:06.810 Well the first step is your browser takes your file and then sends it to your ISP. 01:06.820 --> 01:09.410 So what is an ISP or less less. 01:09.430 --> 01:17.170 You know the ISP here buy a box and a speech or something like Verizon if you're living in the U.S. 01:17.170 --> 01:25.330 or AT&T or you know any service ISP basically X stands for Internet service provider. 01:25.420 --> 01:34.320 So this ISP takes in this Google dot com and they and then says OK you're like your browser is looking 01:34.380 --> 01:37.190 to do you know where Google dot com is. 01:37.200 --> 01:37.960 Right. 01:38.010 --> 01:44.600 So it has a list so it doesn't process called a DNS lookup OK. 01:44.940 --> 01:48.240 So it has a bunch of big big big table. 01:48.300 --> 01:49.070 OK. 01:49.410 --> 01:56.310 And it's not only that the your browser or your ISP that has it's all ISP in the world have it have 01:56.310 --> 01:56.820 it. 01:57.270 --> 02:03.740 And this table is basically made of many fields but the fields we're interested about is the house name 02:06.080 --> 02:09.030 and the IP address. 02:09.140 --> 02:16.340 So you should know that in the Internet any document that is on the Internet has has a unique IP. 02:16.430 --> 02:22.580 So none of the other documents can have the same IP only this document can have that IP just like a 02:22.640 --> 02:27.200 list like a hostname you can't have two web sites which are called Google match.com or you can't have 02:27.200 --> 02:31.780 two web sites that are called you know Facebook dot com. 02:31.820 --> 02:35.720 So each web site has its unique IP address. 02:36.020 --> 02:41.700 So your ISP takes your Google Blackcomb and then says OK I'm. 02:41.840 --> 02:43.090 Is this Google dot com. 02:43.100 --> 02:50.830 No this Housh hostname is not and then looks looks keeps looking until it finds Oh here's Google that. 02:52.790 --> 02:56.130 And then it has some IP was called that IP here. 02:56.330 --> 03:03.190 So it takes that IP address and then says OK I'm going to send it back to your browser. 03:04.590 --> 03:10.810 OK great now your browser takes that IP address some browsers cache it for later. 03:10.830 --> 03:16.110 So that instead of doing this whole process again every time you write google that come your browser 03:16.140 --> 03:19.920 doesn't want to go to your ISP and then make it look for all that. 03:19.920 --> 03:25.220 And that's that's a long process so maybe we can see which Web sites you usually visit like Google dot 03:25.220 --> 03:29.980 com or Facebook if you if you go to Facebook and then it caches it is stores. 03:30.030 --> 03:31.650 But this is not really important. 03:31.700 --> 03:33.430 It's just for your information. 03:33.450 --> 03:37.350 So the important thing is we have this IP address now right. 03:37.380 --> 03:45.620 This IPs with us which is exactly where on the Internet on the worldwide internet you this Google dot 03:45.620 --> 03:46.980 com is located. 03:47.430 --> 03:48.150 OK. 03:48.360 --> 04:01.480 Now your browser takes in this IP and sends and HTP request so it sends an HDTV request. 04:01.850 --> 04:04.230 So what does an HDTV request mean. 04:04.370 --> 04:14.450 What we're going to be talking a lot about it but for now you can get get one of these get or post or 04:14.480 --> 04:16.710 you know there's also a lead. 04:16.860 --> 04:20.800 These put all sort of 80 could be request protocols. 04:20.930 --> 04:29.580 But basically for since you want to access Google dot com then you want to get this Google dot com page. 04:29.660 --> 04:36.400 So you just your browser basically does a get request on that IP address. 04:36.710 --> 04:42.460 And then this IP address is located in a web server. 04:42.620 --> 04:44.740 So this is Google's. 04:45.090 --> 04:45.770 OK. 04:46.680 --> 04:47.690 Web server. 04:47.970 --> 04:49.820 Pretty sure it's much bigger than this. 04:49.830 --> 04:52.440 But let's just assume this is Google's web server. 04:52.450 --> 04:53.830 It's very small. 04:53.910 --> 05:00.930 So once a Google server once the Google server receives your HDTV request and this is very important 05:00.930 --> 05:05.910 right because this is what we're going to be programming in most of the scores once it receives your 05:05.910 --> 05:14.650 request and it takes the request OK and then it prepares a response prepare a response. 05:14.790 --> 05:16.680 So what's the response in this case. 05:16.800 --> 05:21.490 Well that could be the Google or the index. 05:21.760 --> 05:23.570 HVM El-Fadl right. 05:23.610 --> 05:29.190 Because when you when you when you click on the Google dot com enter then you get a page right which 05:29.190 --> 05:35.960 shows you know Google Sites logo and shows the search here and I'm feeling lucky and so on. 05:36.120 --> 05:38.160 So this is basically HMO right. 05:38.160 --> 05:43.990 So in response to you what you're looking for is this page right here index East in MA. 05:44.430 --> 05:50.700 But we're also going to see later in the video that responsa doesn't have to be a page it can be a file 05:50.790 --> 05:58.500 like a Jason or it can be even an SNL file and you don't really care about X a mouse. 05:58.510 --> 06:00.380 What we do care about Jason's. 06:00.480 --> 06:06.230 But just keep in mind that the server receives your request it prepares a response right. 06:06.240 --> 06:12.270 It does some computation inside and it prepares a response and then that response could be you know 06:12.360 --> 06:15.650 any resource basically in a page. 06:15.840 --> 06:24.220 So once we have this response then the server replies you with that response. 06:24.330 --> 06:28.410 So it sends back send back the response. 06:30.930 --> 06:37.710 So once you get the response which is your index issued him out page which for Google then your browser 06:37.710 --> 06:38.210 takes it. 06:38.220 --> 06:43.900 And like oh OK I'm seeing h DeMello so I'm going to change that into a visual form. 06:43.990 --> 06:51.720 And so it takes for example a header or an image for Google for example puts it here and then puts the 06:51.810 --> 06:58.420 text bar here and pushed two buttons over here and basically colors everything just like the indexed 06:58.600 --> 07:01.500 SDMI phials is asking for. 07:01.500 --> 07:08.130 So to recap super quickly your browser once you click Google look on it sends it to if you don't have 07:08.250 --> 07:10.610 google.com stored in your cache. 07:10.620 --> 07:12.290 Then you need to go to your ISP. 07:12.300 --> 07:15.510 Your ISP does a DNS lookup for you. 07:15.510 --> 07:22.980 It gets the IP for that Web site and then you take that IP address you send that HTP request to the 07:22.980 --> 07:30.060 server which is indicated by this IP address and then the server prepares a response for you which could 07:30.060 --> 07:33.530 be an index of each DML Jaison which we're about. 07:33.540 --> 07:34.830 Talk about a lot. 07:34.830 --> 07:39.850 And then once it has this response then it sends it back to you. 07:40.350 --> 07:44.350 And that's basically the whole process off you know. 07:44.430 --> 07:52.080 And usually people who write this are called web or back and engineers so people who handle these types 07:52.080 --> 07:56.380 of back and stuff on the servers are called back and engineers. 07:56.670 --> 08:04.350 So most of our work is actually going to be in this case in this year regarding where we're building 08:04.410 --> 08:06.870 and the API or a web service. 08:06.900 --> 08:09.590 So we're getting a request from other people. 08:09.810 --> 08:15.810 We have to parse their request understand what they're what they're asking us to do and then prepare 08:15.810 --> 08:20.780 that response which in our case is going to be a Jasen not a index of HMO. 08:21.150 --> 08:25.330 So we're prepared a response and we send it back to them so that they're happy. 08:25.350 --> 08:25.670 Right. 08:25.680 --> 08:35.050 Whether there are customers or or employer whether OK so in the previous video we both are using flask. 08:35.200 --> 08:42.670 We built a web app web service which basically when we wrote we wrote that your L went to seven point 08:42.670 --> 08:44.910 zero point zero point one. 08:45.520 --> 08:48.060 Five thousand I remember. 08:48.220 --> 08:49.770 Slash OK. 08:50.260 --> 08:53.820 And then once we clicked that then we saw Hello world. 08:53.830 --> 08:56.080 So what really happened here. 08:56.080 --> 09:05.890 Well once we wrote this you are all in this in in our browser this you are actually is a very special 09:05.890 --> 09:07.500 type of IP. 09:07.510 --> 09:10.300 This is an IP here. 09:10.510 --> 09:13.710 This IP is basically our local host. 09:13.900 --> 09:17.330 So our local host means it's our own computer. 09:17.380 --> 09:20.150 So this IP response to our own computer. 09:20.320 --> 09:26.080 So we don't need to do any DNS look up on this on this IP here because we already know where where it's 09:26.080 --> 09:26.580 from. 09:26.590 --> 09:27.490 Right. 09:27.550 --> 09:36.290 So when we did flask run the flask is very nice because flask has already in it a web server. 09:36.430 --> 09:40.830 So once we click flask run then it sets up a web server for us. 09:41.900 --> 09:51.080 So at the Y runs on the server sets up a local server and its location is one to seven point zero point 09:51.080 --> 09:52.000 zero point one. 09:52.130 --> 09:56.230 And it's listening on 4 x 5000. 09:56.280 --> 10:05.170 So once I click this that actually my browser sent my HTC request to my computer my own computer. 10:05.550 --> 10:15.360 So my browser sends that HTP request to my server here which is at IPY now my X Y gets this request 10:16.460 --> 10:23.640 and then says OK if I get a request at slash which is here we're getting a request at slash right. 10:23.960 --> 10:30.660 If I get a request at slash then I'm going to return the user simply Hello world. 10:32.740 --> 10:35.260 So hear this hello world. 10:35.290 --> 10:38.470 Is our response that we prepared right. 10:38.470 --> 10:40.110 Very short response. 10:40.540 --> 10:45.560 And then once we return this response then it takes it back to our browser. 10:45.580 --> 10:50.080 So this is our browser here and then our browser displayed it for us. 10:50.080 --> 10:51.340 And it showed. 10:51.340 --> 10:52.830 Hello world. 10:53.650 --> 10:55.390 Displayed on the screen. 10:56.020 --> 10:59.120 So to recap flask is supersmart. 10:59.140 --> 11:03.930 It has inside of it built in server so we don't need to know where. 11:03.930 --> 11:09.460 We're still basically learning and developing something off line so we don't want to have to keep putting 11:09.460 --> 11:16.660 it on our real online server deploy everything and then code there is going to be very tedious to just 11:16.660 --> 11:21.540 change something and then put all the code again on that web server she's on line here. 11:21.730 --> 11:26.570 And then test it and then change a few lines and then put it here. 11:26.620 --> 11:28.500 So this is a very tedious process. 11:28.500 --> 11:31.950 So instead what we do is we do a local server. 11:32.020 --> 11:33.990 So we set up a server on our machine. 11:34.000 --> 11:41.920 We simulate what would happen if this application was online and then we say if I get a request at my 11:41.920 --> 11:43.950 own computer from my own computer. 11:43.950 --> 11:51.620 Notice that nobody can access this year except you if you get this you are here to anybody outside. 11:51.790 --> 11:56.240 Then you would basically be going to his own computers localhost. 11:56.260 --> 11:58.400 So it doesn't make any sense right. 11:58.900 --> 12:03.050 So nobody can access this except use only for testing purposes. 12:03.070 --> 12:09.670 So once you get a request on this your browser sends a request to this IP which is which is basically 12:09.670 --> 12:16.420 a server that is listening there and then it picks up and up you picks up the request it returns. 12:16.420 --> 12:17.260 Hello world. 12:17.260 --> 12:22.720 It parses the request and it returns the response and then the response is given to the browser and 12:22.720 --> 12:24.350 it's displayed on the browser. 12:25.410 --> 12:27.530 So yeah hopefully this video was clear. 12:27.540 --> 12:28.880 Make sure you understand it. 12:28.890 --> 12:34.920 One hundred thousand percent before going on to the next videos because this is really one of the most 12:34.920 --> 12:40.800 important videos in the whole tutorial because if you understand this then you would understand the 12:40.800 --> 12:46.250 whole process and off of the whole development cycle that we're going to go through. 12:46.650 --> 12:51.270 So hopefully this video is clear if you have any questions on this section. 12:51.270 --> 12:54.180 Make sure to put it on the queue and they don't. 12:54.180 --> 12:59.240 Don't move forward until you understand this whole Web Web site go from scratch. 12:59.620 --> 13:00.260 Yeah. 13:00.690 --> 13:03.250 Thanks for watching and I'll see you in the next video.