Advance Praise for Head First Python Part 6 doc

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web development

You can put your program on the Web

You’ll want to be

able to share your

functionality with lots

of people...

...but you probably want

only one version of your

program “out there” that

everyone accesses...

...and you need to make sure

updates to your program

are easy to apply.

A “webapp” is what you want.

If you develop your program as a Web-based application (or webapp, for short),

your program is:

• Available to everyone who can get to your website

• In one place on your web server

• Easy to upate as new functionality is needed

But…how do webapps actually work?

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anatomy of a web request

Webapps Up Close

The Internet

I just type the

web address into my

browser’s location bar

Step 1: Your user enters and press Enter... a web address, selects

a hyperlink, or clicks a

button in her chosen

web browser.

No matter what you do on the Web, it’s all about requests and responses. A web request is sent

from a web browser to a web server as the result of some user interaction. On the web server, a

web response (or reply) is formulated and sent back to the web browser. The entire process can

be summarized in five steps.

Step 2: The web

browser converts

the user’s action

into a web request

and sends it to a

server over the

Internet.

Hey, hello there...what’s this?

A web request just for me? How

nice...

Step 3: The web server

receives the web request

and has to decide what

to do next.

Web

Server

Deciding what to do next

One of two things happen at this point. If the web request

is for static content—such as an HTML file, image, or

anything else stored on the web server’s hard disk—the web

server locates the resource and returns it to the web browser as

a web response.

If the request is for dynamic content—that is, content that

must be generated—the web server runs a program to produce

the web response.

Here comes a web

request.

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web development

The Internet

That’s exactly what I

need. Thanks!

Step 4: The web server

processes the web

request, creating a web

response, which is sent

back over the Internet

to the waiting web

browser.

Web

Server

Step 5: The web

browser receives the

web response and

displays it on your

user’s screen.

The (potentially) many substeps of step 4

In practice, step 4 can involve multiple substeps, depending

on what the web server has to do to produce the response.

Obviously, if all the server has to do is locate static content

and sent it back to the browser, the substeps aren’t too

taxing, because it’s all just file I/O.

However, when dynamic content must be generated, the sub￾steps involve the web server locating the program to execute,

executing the located program, and then capturing the output

from the program as the web response…which is then sent

back to the waiting web browser.

This dynamic content generation process has been

standardized since the early days of the Web and is known

as the Common Gateway Interface (CGI). Programs

that conform to the standard are often referred to as CGI

scripts.

Here comes a web

response.

Here you go...a web

response generated just for

you. Enjoy!

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webapp requirements

What does your webapp need to do?

Let’s take a moment to consider what you want your webapp to look like

and how it should behave on your user’s web browser. You can then use this

information to help you specify what your webapp needs to do.

I guess I need a nice,

friendly home page to

kick things off, eh?

Yeah...and I want to be

able to get at my times

easily...

...and once I’ve

selected mine, I want

them to look nice on

my screen, so I can print

them for my mom.

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web development

There’s nothing like grabbing your pencil and a few blank paper

napkins to quickly sketch a simple web design. You probably

need three web pages: a “welcome” page, a “select an athlete”

page, and a “display times” page. Go ahead and draw out a rough

design on the napkins on this page, and don’t forget to draw any

linkages between the pages (where it makes sense).