1 00:00:00,450 --> 00:00:01,000 Hello. 2 00:00:01,010 --> 00:00:04,480 And in this lecture you will build your first Website 3 00:00:04,530 --> 00:00:08,050 with Flask if you haven't done so already. 4 00:00:08,280 --> 00:00:15,120 And Flask is a Python framework that has all the tools and the templates and the functions for you to 5 00:00:15,120 --> 00:00:17,510 build a website with Python. 6 00:00:17,910 --> 00:00:24,630 And before going deeper into Flask and explaining you hold to this Flask probably for a building Python 7 00:00:24,630 --> 00:00:25,430 web apps, 8 00:00:25,620 --> 00:00:33,030 I'd like you to spend three minutes to be with a very basic web site with Flask and that is done with 9 00:00:33,030 --> 00:00:35,950 only Seven lines of Python code. 10 00:00:36,060 --> 00:00:40,710 So that's what we'll do right now. To build a web app with Flask, 11 00:00:40,710 --> 00:00:49,380 you need to have Flask installed, so pip install flask should use the whole Flask in your Python 12 00:00:49,380 --> 00:00:49,920 environment. 13 00:00:53,610 --> 00:00:54,190 All right. 14 00:00:54,200 --> 00:00:59,330 That was successfully installed and let's create our website now. 15 00:00:59,930 --> 00:01:02,720 What you need is a python file. 16 00:01:04,160 --> 00:01:05,830 So I'm creating one here. 17 00:01:05,990 --> 00:01:08,090 Let's say script1.py. 18 00:01:08,140 --> 00:01:15,320 And then here is where you write the code that will build your web app and everything starts from 19 00:01:15,320 --> 00:01:17,000 importing Flask. 20 00:01:17,000 --> 00:01:24,460 And actually you don't import the flask framework but you import the Flask class from the flask framework. 21 00:01:24,500 --> 00:01:33,070 So from flask import Flask and flask is a class of this library. 22 00:01:33,350 --> 00:01:38,840 And this contains all the prototypes that you need to build web apps with Python. 23 00:01:39,470 --> 00:01:41,360 So this will handle requests for you. 24 00:01:41,360 --> 00:01:47,780 You don't have to set up requests yourself, but let's focus on this example for now. 25 00:01:47,900 --> 00:01:50,480 Once you do that, you need to create a variable 26 00:01:50,480 --> 00:01:55,200 where you'll store your flask object instance, your flask application. 27 00:01:55,220 --> 00:02:01,960 That would be equal to the Flask class and you pass the name variable in there. 28 00:02:01,970 --> 00:02:04,460 Just don't worry about that right now. 29 00:02:05,930 --> 00:02:09,900 Then you need a decorator, route. 30 00:02:09,930 --> 00:02:14,580 And here is the URL where you will view your Website. 31 00:02:14,630 --> 00:02:17,530 So this slash here means the home page. 32 00:02:18,830 --> 00:02:22,630 And just after that you needed to write the function. 33 00:02:22,630 --> 00:02:29,240 The python function and this function is what defines what your web page will do. 34 00:02:29,630 --> 00:02:31,940 In this case we will return a string. 35 00:02:34,990 --> 00:02:36,590 Let's say this string here. 36 00:02:37,010 --> 00:02:40,910 "Website content goes here". Just after that 37 00:02:40,920 --> 00:02:43,010 you need two more lines of code. 38 00:02:43,100 --> 00:02:50,620 That's a conditional statement. If name equals the string main 39 00:02:53,900 --> 00:02:54,380 app.run 40 00:02:54,430 --> 00:02:59,630 (debug) equals True. 41 00:02:59,630 --> 00:03:00,600 That's it. 42 00:03:00,620 --> 00:03:02,150 Don't worry about this 43 00:03:02,160 --> 00:03:02,830 right now. 44 00:03:02,840 --> 00:03:11,600 Just click Save, open the terminal and execute a script with Python, script1 Python. 45 00:03:14,850 --> 00:03:19,930 And it looks like your web app is running now so open the browser. 46 00:03:20,640 --> 00:03:24,090 And your web website should be live or your local host. 47 00:03:26,150 --> 00:03:27,200 That's it. 48 00:03:27,200 --> 00:03:33,840 Nothing impressive, but you see how easy is to create a Website with Python. 49 00:03:33,880 --> 00:03:38,940 And in this case we are just returning a string here to the Website. 50 00:03:39,690 --> 00:03:46,520 So there's nothing fancy in there but later on I'll explain to you how you can return HTML pages 51 00:03:46,670 --> 00:03:53,480 instead of plain Python strings to your Website. That will allow you to actually have different formats 52 00:03:53,480 --> 00:04:00,260 different fonts on your text and then you can also apply CSS styling to your HTML, and so you will 53 00:04:00,260 --> 00:04:04,050 have a complete Website with modern features. 54 00:04:04,070 --> 00:04:09,360 For now, let's make sure you understand these seven lines of code. 55 00:04:09,930 --> 00:04:11,500 It's seven lines. 56 00:04:11,540 --> 00:04:18,410 As I said the first line you are importing the Flask class object from the flask library. 57 00:04:18,530 --> 00:04:19,990 Then in the next line. 58 00:04:20,010 --> 00:04:24,230 Once you have imported the Flask class in here, the Flask object 59 00:04:24,230 --> 00:04:29,670 in other words, you are instantiating that class that object. 60 00:04:29,690 --> 00:04:35,650 This here is a special variable that will get as value the name of the python script. 61 00:04:35,660 --> 00:04:44,180 Now when you execute a Python file, a Python script, Python assigns the name main, this string to the file. 62 00:04:47,780 --> 00:04:51,980 When you import a script into another script, 63 00:04:51,980 --> 00:04:58,780 like if we import this script from another script, this script we will be assigned the script1.py 64 00:04:58,770 --> 00:05:02,350 name, but when you execute the script 65 00:05:02,360 --> 00:05:08,000 Python assigns the name __main__. 66 00:05:08,420 --> 00:05:20,390 So what happens is that in this line we say if name equals to main, then run the app, and this is true 67 00:05:20,390 --> 00:05:23,990 when we execute the script as we did here. 68 00:05:24,770 --> 00:05:30,710 But, if we imported this script from another script this line here would not be executed. 69 00:05:31,190 --> 00:05:37,480 So this allows us to have control over this script using this line here. 70 00:05:37,620 --> 00:05:40,210 Then we have these two lines. 71 00:05:40,340 --> 00:05:42,770 This is a decorator. 72 00:05:43,010 --> 00:05:49,280 Now the output that this function produces will be mapped to this URL. 73 00:05:49,370 --> 00:05:52,970 So if you want you can change this URL to this for example. 74 00:05:52,970 --> 00:05:57,150 Save the script, sure you need a URL here. 75 00:05:58,250 --> 00:06:07,950 Save the script, run and go to the local hosts, reload and this time you'll get an error, Python couldn't 76 00:06:07,970 --> 00:06:13,760 find this page but it can't find the about page. 77 00:06:14,750 --> 00:06:16,370 That's it. 78 00:06:16,370 --> 00:06:24,020 If you still want a Homepage you'd add another decorator and another function just after the decorator. 79 00:06:25,130 --> 00:06:37,520 So just leave it as the home page and just say "Homepage" here, save. 80 00:06:37,640 --> 00:06:45,770 Again we have an error because we cannot have functions with the same name, so we can change this to about, 81 00:06:45,770 --> 00:06:47,510 the name doesn't matter. 82 00:06:47,540 --> 00:06:58,560 So this doesn't have to be the same with this one, click save, run the script again and go to the website. 83 00:06:59,540 --> 00:07:02,180 This is working. 84 00:07:02,180 --> 00:07:04,580 Try the Homepage. 85 00:07:04,580 --> 00:07:07,970 This is working too. If you want to change something. 86 00:07:08,010 --> 00:07:13,000 Let's say "About content goes here!". 87 00:07:13,040 --> 00:07:18,330 You save the script and the web app will start by itself. 88 00:07:18,380 --> 00:07:24,630 So you don't have to close the web app and run the script again as I did earlier. 89 00:07:24,740 --> 00:07:29,230 If you get an error like I got previously, the script will stop. 90 00:07:29,420 --> 00:07:32,320 But if everything is all right you will not get an error. 91 00:07:32,490 --> 00:07:39,000 So, try this again. Homepage is fine. 92 00:07:39,230 --> 00:07:42,380 The about page is fine too. 93 00:07:42,390 --> 00:07:50,060 And with the new content. So that's about it. In the next lecture, you'll learn how to return 94 00:07:50,090 --> 00:07:58,130 an HTML template, an HTML file using your Python functions, that will give you full power to publish anything that 95 00:07:58,130 --> 00:08:05,690 you want on your website and not just plain strings as we did in this lecture. 96 00:08:05,740 --> 00:08:07,500 See you in the next lecture.