Showing Revision 11 created 09/03/2017 by Dejan Trajkovic.

1. Title:
   Hello Webapp World - Web Development
2. Description:

3. 0 0:00 - 0:03
   Okay, so let's move on to some live web applications.
4. 3000 0:03 - 0:06
   So, at the end of your last homework, you should have
5. 6000 0:06 - 0:10
   Google App Engine running on your machine, and you should have a basic site online.
6. 10000 0:10 - 0:14
   We're going to start with basically the simple hello world example
7. 14000 0:14 - 0:17
   that Google has on their site, which I have.
8. 17000 0:17 - 0:22
   This is the main hello world Python file from the Google App Engine example page,
9. 22000 0:22 - 0:24
   and it's got 2 main sections.
10. 24000 0:24 - 0:26
    We'll start with this section down here at the bottom.
11. 26000 0:26 - 0:29
    This is the URL mapping section, and in this case,
12. 29000 0:29 - 0:33
    we have 1 URL, slash, and it maps to a handler called MainPage.
13. 33000 0:33 - 0:36
    MainPage is defined in this class called MainPage.
14. 36000 0:36 - 0:41
    It inherits from webapp to RequestHandler, which is the generic
15. 41000 0:41 - 0:43
    request handler from Google.
16. 43000 0:43 - 0:46
    If you don't know what classes are, you can learn about them offline.
17. 46000 0:46 - 0:50
    It's basically a convenient way for grouping together
18. 50000 0:50 - 0:52
    functions and data that are all related to the same thing.
19. 52000 0:52 - 0:54
    We're not going to spend a whole lot of time on it here,
20. 54000 0:54 - 0:56
    but you should be able to keep up just fine.
21. 56000 0:56 - 0:58
    Our class has a function called get, which takes a parameter called self,
22. 58000 0:58 - 1:04
    which is the common first parameter to most Python methods.
23. 64000 1:04 - 1:07
    So, this function does 2 things.
24. 67000 1:07 - 1:12
    First, it takes self.response, which is the kind of global response object
25. 72000 1:12 - 1:16
    that this framework uses, and it sets a header.
26. 76000 1:16 - 1:20
    It sets the Content-Type header to equal text/plain.
27. 80000 1:20 - 1:24
    By default, the content type is text/html, but in this case it's setting it to text/plain,
28. 84000 1:24 - 1:28
    and then it's writing the string "Hello, webapp World!"
29. 88000 1:28 - 1:32
    If we start up Google App Engine, I'll start Google App Engine in my terminal here,
30. 92000 1:32 - 1:37
    and then I'll go to my browser and load the page, and this is what we see.
31. 97000 1:37 - 1:42
    We see that string that our program was writing out in our browser, "Hello, webapp World!"
32. 102000 1:42 - 1:46
    Pretty neat.